Impact of the IVF laboratory environment on human preimplantation embryo phenotype

METTL7A improves bovine IVF embryo competence by attenuating oxidative stress†

In vitro fertilization is a widely used assisted reproductive technology to achieve a successful pregnancy. However, the acquisition of oxidative stress in embryo in vitro culture impairs its competence. Here, we demonstrated that a nuclear coding gene, methyltransferase-like protein 7A, improves the developmental potential of bovine embryos. We found that exogenous methyltransferase-like protein 7A modulates expression of genes involved in embryonic cell mitochondrial pathways and promotes trophectoderm development. Surprisingly, we discovered that methyltransferase-like protein 7A alleviates mitochondrial stress and DNA damage and promotes cell cycle progression during embryo cleavage. In summary, we have identified a novel mitochondria stress eliminating mechanism regulated by methyltransferase-like protein 7A that occurs during the acquisition of oxidative stress in embryo in vitro culture. This discovery lays the groundwork for the development of methyltransferase-like protein 7A as a promising therapeutic target for in vitro fertilization embryo competence.

Mineral oil viscosity and quantity impact osmotic pressure, not embryo development

Dry incubators prevent bacterial growth and allow time-lapse imaging. However, they cause more significant osmotic pressure changes in the culture medium than in humidified incubators. Few reports have explored the effect of osmotic pressure on human embryos cultured under different conditions. This study examined how changes in osmotic pressure affect human embryos in a dry incubator. The study incubated embryos in culture mediums covered with mineral oil of varying viscosities and quantities. The osmotic pressure of the culture medium was measured daily for six-day period (Day 0-6) in four experimental groups established by varying the viscosity and volume of mineral oil: low viscosity (Light), 3.0 ml or 4.5 ml, and high viscosity (Heavy), 3.0 ml or 4.5 ml of mineral oil. The Light 3.0 ml and Heavy 4.5 ml groups, showing the greatest difference in the osmotic pressure, were used to culture of human embryos. After six days of incubation, the osmotic pressure increased the most in Light 3.0 ml group. Heavy 4.5 ml group had the smallest change. However, no significant differences were noted in the formation rates of blastocysts, good-quality blastocysts, or cell count between the two groups. The study suggests that even when the culture medium is covered with heavy mineral oil in a dry incubator, osmotic pressure increases after six days but does not significantly affect the formation of blastocysts. These findings provide valuable insights into the effects of varying osmotic pressure on embryonic development and may help in optimizing conditions for in vitro fertilization.

Advanced strategies for single embryo selection in assisted human reproduction: A review of clinical practice and research methods

Among the primary objectives of contemporary assisted reproductive technology research are achieving the births of healthy singletons and improving overall fertility outcomes. Substantial advances have been made in refining the selection of single embryos for transfer, with the aim of maximizing the likelihood of successful implantation. The principal criterion for this selection is embryo morphology. Morphological evaluation systems are based on traditional parameters, including cell count and fragmentation, pronuclear morphology, cleavage rate, blastocyst formation, and various sequential embryonic assessments. To reduce the incidence of multiple pregnancies and to identify the single embryo with the highest potential for growth, invasive techniques such as preimplantation genetic screening are employed in in vitro fertilization clinics. However, new approaches have been suggested for clinical application that do not harm the embryo and that provide consistent, accurate results. Noninvasive technologies, such as time-lapse imaging and omics, leverage morphokinetic parameters and the byproducts of embryo metabolism, respectively, to identify noninvasive prognostic markers for competent single embryo selection. While these technologies have garnered considerable interest in the research community, they are not incorporated into routine clinical practice and still have substantial room for improvement. Currently, the most promising strategies involve integrating multiple methodologies, which together are anticipated to increase the likelihood of successful pregnancy.

One-step warming of vitrified human cleavage and blastocyst stage embryos does not adversely impact embryo survivability and subsequent developmental potential

STUDY QUESTION

Does one-step warming (OW), a simplified embryo warming protocol, adversely affect survival and developmental potential in vitrified cleavage or blastocyst stage embryos compared to standard multi-step warming (SW)?

SUMMARY ANSWER

OW showed no detrimental effects on survival and developmental potential compared to SW in cleavage and blastocyst stage embryos.

WHAT IS KNOWN ALREADY

While standard embryo warming protocols involve a multi-step procedure using a stepwise osmotic solution to avoid a rapid influx of water into the embryo, recent studies suggest that eliminating the stepwise warming process does not reduce embryo survival and embryo transfer outcomes. However, previous reports have focused primarily on pregnancy rates, and a more detailed analysis of the effects of rapid osmotic pressure changes on embryos is necessary to standardize the protocol.

STUDY DESIGN, SIZE, DURATION

This preliminary study includes donated 377 vitrified human embryos (177 cleavage and 200 blastocyst stage) from 210 patients approved for discard at the patient's consent. The embryos were randomly allocated and warmed using either SW or OW protocols. In the SW protocol, embryos were rinsed with a stepwise osmotic solution (thawing, dilution, and washing solutions), and the process was completed with a 13-min warming period. In the OW protocol, embryos were only rinsed in a single solution (thawing solution) for 1 min.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Post-warming embryos were cultured using a time-lapse incubator. Survival rate and developmental potential, including the occurrence of abnormal morphokinetics and the time required for blastocyst formation after warming of cleavage stage embryos, were compared between SW and OW. Embryos that developed into the blastocyst stage were morphologically evaluated. In the warming of blastocyst stage embryos, the survival rate was determined by the presence of blastocoel expansion, and the proportion of full re-expanded blastocysts was observed at 3- and 24-h post-warming. An in vitro adhesion assay was also performed on blastocysts after culture, and adhesion rate and outgrowth area were measured 24, 48, and 72 h after culture with fibronectin-precoated dishes.

MAIN RESULTS AND THE ROLE OF CHANCE

OW did not negatively impact survival rates in either cleavage (100% in both OW and SW groups) or blastocyst stage embryos (99% in both groups). Cleavage stage embryos warmed by OW had superior or comparable rates of morulation (96 vs 85%, P = 0.0387), blastulation (78 vs 73%, P = 0.4044), full-blastocyst formation (60 vs 53%, P = 0.3196), and expanded-blastocyst formation (56 vs 49%, P = 0.4056) compared to those warmed by SW. Time-lapse monitoring analysis revealed that the frequency of collapses was reduced in OW (30 vs 50%, P = 0.0410). Additionally, all other abnormal morphokinetics were equivalent between OW and SW (P > 0.05); moreover, the time required for blastocyst formation (P > 0.05) and the morphological quality after development into the blastocyst stage (P > 0.05) were not significantly different between OW and SW. In warming of blastocyst stage embryos, the time required for full re-expansion was longer with OW (3.20 ± 3.03 h vs 2.14 ± 2.17 h, P = 0.0008), but there was no significant difference in the proportion of full re-expanded blastocysts at 3- (67 vs 75%, P = 0.2417) and 24-h (98 vs 97%, P = 1.0000) post-warming. The in vitro adhesion assay showed no significant differences in adhesion rate and outgrowth area at all observation points (P > 0.05).

LIMITATIONS, REASONS FOR CAUTION

This study was carried out as a preliminary trial using discarded embryos, which limited the number of embryos analyzed. Additionally, the impact on embryo transfer outcomes, such as clinical pregnancy and livebirth rates, remains unclear.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings suggest that OW is a safe and efficient alternative to SW protocols and may improve the efficiency of IVF laboratory workflow without impairing embryo potentials.

STUDY FUNDING/COMPETING INTEREST(S)

No funding was obtained for this study. The authors have no conflicts of interest to declare related to this study.

TRIAL REGISTRATION NUMBER

N/A.

Culture media with antioxidants improved preimplantation embryo development and clinical outcomes of patients of advanced age

RESEARCH QUESTION

What are the clinical effects of using culture media supplemented with antioxidants (AOX) throughout the IVF process?

DESIGN

Prospective randomized single-centre study. Cumulus-oocyte complexes and semen samples collected from 127 treatment cycles were divided evenly between the study arm (culture media with AOX) and the control arm (culture media without AOX). The primary endpoint was the good-quality blastocyst (GQB) rate on day 5-6 per metaphase II (MII) oocyte.

RESULTS

Fertilization rate and day 5-6 blastocyst rate per MII oocyte differed significantly in favour of the study arm, whereas GQB rate did not. A subgroup analysis, stratified by maternal age, revealed significant improvements in the study arm for day 3 embryo development rate, day 5-6 blastocyst rate, GQB rate and blastocyst utilization rate for patients aged 35-40 years, while the impacts on these endpoints were much smaller in patients aged <35 years. Ninety-four single vitrified blastocyst transfers (SVBT) were performed in each arm. The blastocysts derived from the study arm showed better results of SVBT for patients aged 35-40 years, defined by embryo implantation rate, fetal heartbeat rate and live birth rate, whereas these variables did not differ significantly between the two arms when assessing the results for patients of all ages and patients aged <35 years.

CONCLUSIONS

Embryo development and SVBT outcomes of treatment cycles of patients aged 35-40 years improved significantly when using AOX-supplemented culture media throughout the IVF process.

METTL7A improves bovine IVF embryo competence by attenuating oxidative stress

In vitro fertilization (IVF) is a widely used assisted reproductive technology to achieve a successful pregnancy. However, the acquisition of oxidative stress in embryo in vitro culture impairs its competence. Here, we demonstrated that a nuclear coding gene, methyltransferase-like protein 7A (METTL7A), improves the developmental potential of bovine embryos. We found that exogenous METTL7A modulates expression of genes involved in embryonic cell mitochondrial pathways and promotes trophectoderm development. Surprisingly, we discovered that METTL7A alleviates mitochondrial stress and DNA damage and promotes cell cycle progression during embryo cleavage. In summary, we have identified a novel mitochondria stress eliminating mechanism regulated by METTL7A that occurs during the acquisition of oxidative stress in embryo in vitro culture. This discovery lays the groundwork for the development of METTL7A as a promising therapeutic target for IVF embryo competence.

In vitro fertilization, intracytoplasmic sperm injection, in vitro maturation, and embryo culture

Infertility is a highly prevalent disease affecting 1 in 6 couples worldwide. While there are numerous treatment options available to treat infertility, in vitro fertilization (IVF) is the most successful therapy available. IVF traditionally involves superovulation of the ovaries followed by ultrasound (US)-guided oocyte retrieval, fertilization of oocytes in vitro, and culture of resultant embryos. Embryo(s) are then either transferred into the uterus or cryopreserved. There have been tremendous advances in each step of this process over the past 40 years, however, much work still remains to be done. This review discusses the history and current techniques involved in oocyte fertilization and embryo culture. Highlighted areas include conventional insemination and intracytoplasmic sperm injection (ICSI), embryo culture, and laboratory assessment. Areas of past and present research including time-lapse imaging and in vitro maturation are also discussed.

Clinical pregnancy rates after blastocyst culture at a stable temperature of 36.6°C versus 37.1°C: a prospective randomized controlled trial

STUDY QUESTION

Is there a difference in clinical pregnancy rates (CPRs) in good prognosis patients after single embryo transfer (SET) on Day 5, in case of stable culture at 36.6°C or 37.1°C?

SUMMARY ANSWER

CPR (with heartbeat at 7 weeks) after blastocyst transfer do not differ after culturing at 36.6°C or 37.1°C.

WHAT IS KNOWN ALREADY

Since the beginning of IVF, embryo culture has been performed at 37.0°C; however, the optimal culture temperature remains unknown. Changes in incubator types have led to significant improvements in temperature control. Stable temperature control, i.e. with temperature differences of max. 0.1°C between chambers, is possible in some incubators. A previous prospective pilot study showed that embryo development on Day 5/6 was not affected when embryos were cultured at a stable temperature of 36.6°C or 37.1°C, but culture at 37.1°C resulted in an increased CPR when compared to culture at 36.6°C (74.2% vs 46.4%).

STUDY DESIGN, SIZE, DURATION

A prospective randomized controlled trial was performed in a tertiary fertility centre between February 2017 and November 26, 2022. A sample size of 89/89 patients with fresh single embryo transfer (SET) was required to achieve 80% power to detect a difference of 0.22 between group proportions (0.43-0.65) at a significance level of 0.05 using a two-sided z-test with continuity correction.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Patients were recruited on the day of oocyte retrieval based on inclusion criteria with final randomization after denudation once six mature oocytes were present. The primary endpoint was CPR (heartbeat at 7 weeks); secondary endpoints were fertilization rate, blastocyst development, biochemical pregnancy rate, live birth rate (LBR), and cumulative live birth rate (CLBR).

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 304 patients were eligible for the study; of these 268 signed the consent, 234 (intention-to-treat) were randomized and 181 (per-protocol) received a SET on Day 5: 90 received culture at 36.6°C and 91 at 37.1°C. Patients were on average 32.4 ± 3.5 versus 32.5 ± 4.2 years old, respectively. No differences were observed in embryological outcomes per cycle between culture at 36.6°C versus 37.1°C: 12.0 ± 3.8 vs 12.1 ± 3.8 COCs retrieved (P = 0.88), 10.0 ± 3.1 versus 9.9 ± 2.9 mature oocytes inseminated (P = 0.68), with a maturation rate of 84.2% (901/1083) versus 83.5% (898/1104) (P = 0.87); and 8.0 ± 3.1 versus 7.9 ± 2.7 normally fertilized oocytes with a fertilization rate of 79.7% (720/901) vs 80.5% (718/898) (P = 0.96), respectively. On average 1.5 ± 1.7 versus 1.4 ± 1.9 (P = 0.25) and 1.1 ± 1.1 versus 0.9 ± 1.0 (P = 0.45) supernumerary blastocysts were vitrified on Day 5 and Day 6, respectively. The utilization rate per fertilized oocyte was 46.1% vs 41.5% (P = 0.14). A SET was performed for 181 patients, leading to a biochemical pregnancy rate of 72.2% (65/90) versus 62.7% (57/91) (P = 0.17), respectively. The CPR per fresh transfer cycle was 51.1% (46/90) versus 48.4% (44/91) [OR (95% CI) 1.11 (0.59-2.08), P = 0.710]. To date, a CLBR of 73.3% (66/90) versus 67.0% (61/91) (P = 0.354) has been observed, respectively. In each group, seven patients without live birth have remaining blastocysts frozen. The CPR for the intention-to-treat groups were 38.3% vs 38.6% [OR (95% CI) 0.98 (0.56-1.73), P = 0.967], respectively, for culture at 36.6°C versus 37.1°C.

LIMITATIONS, REASONS FOR CAUTION

Only selected patients with expected good prognosis were eligible for the study.

WIDER IMPLICATIONS OF THE FINDINGS

Embryos tend to tolerate small changes in temperature deviations during culture to the blastocyst stage, as demonstrated by their similar implantation potential at two slightly different temperatures.

STUDY FUNDING/COMPETING INTEREST(S)

There is no funding or conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

NCT03548532.

TRIAL REGISTRATION DATE

23 October 2017.

DATE OF FIRST PATIENT’S ENROLMENT

10 November 2017.

Temperature fluctuations during embryo transfer can be mitigated by optimizing transfer protocol

RESEARCH QUESTION

What impact do variations in embryo transfer catheter loading and movement procedures have on temperature and pH fluctuations during embryo transfer?

DESIGN

Mock embryo transfers were conducted to test the impact of air flow/movement, use of catheter coverings, and the type of workstation used for catheter loading on catheter temperature. A thermocouple probe inserted into the tip of the outer catheter or taped to the exterior of the inner catheter recorded temperature within the catheter every 5 s from time of mock embryo loading (TL) to 60 s (TL + 60 s) or from the start of transit (TT). Fluctuations in culture medium pH in embryo transfer dishes were monitored.

RESULTS

The rate of cooling during transit was faster (all P < 0.05) when catheters were uncovered compared with all covering methods tested. This resulted in a lower catheter temperature at TL + 20 s (28.43 ± 0.30 °C) compared with catheters covered by plastic tubing (31.4 ± 0.30 °C), paper (31.0 ± 0.26 °C) or paper + thumb (31.1 ± 0.78 °C; all P ≤ 0.05). Temperature was maintained more effectively when catheters were loaded in a crib compared with a heated stage, until initiation of transit, when the rate of temperature decrease was similar. Culture medium pH increased more rapidly when embryo transfer dishes remained on a heated stage during the procedure compared with in an open crib.

CONCLUSIONS

Temperature loss during the embryo transfer procedure can be mitigated by reducing the transit time and using catheter coverings. Use of a crib for catheter loading only improved temperature stability while the catheter remained in the crib, not during transit, and reduced pH fluctuations during the procedure.

Reactive oxygen species signalling in the deterioration of quality of mammalian oocytes cultured in vitro: Protective effect of antioxidants

The in vitro fertilization (IVF) is the first choice of infertile couples worldwide to plan for conception. Besides having a significant advancement in IVF procedure, the success rate is still poor. Although several approaches have been tested to improve IVF protocol, minor changes in culture conditions, physical factors and/or drug treatment generate reactive oxygen species (ROS) in oocytes. Due to large size and huge number of mitochondria, oocyte is more susceptible towards ROS-mediated signalling under in vitro culture conditions. Elevation of ROS levels destabilize maturation promoting factor (MPF) that results in meiotic exit from diplotene as well as metaphase-II (M-II) arrest in vitro. Once meiotic exit occurs, these oocytes get further arrested at metaphase-I (M-I) stage or metaphase-III (M-III)-like stage under in vitro culture conditions. The M-I as well as M-III arrested oocytes are not fit for fertilization and limits IVF outcome. Further, the generation of excess levels of ROS cause oxidative stress (OS) that initiate downstream signalling to initiate various death pathways such as apoptosis, autophagy, necroptosis and deteriorates oocyte quality under in vitro culture conditions. The increase of cellular enzymatic antioxidants and/or supplementation of exogenous antioxidants in culture medium protect ROS-induced deterioration of oocyte quality in vitro. Although a growing body of evidence suggests the ROS and OS-mediated deterioration of oocyte quality in vitro, their downstream signalling and related mechanisms remain poorly understood. Hence, this review article summarizes the existing evidences concerning ROS and OS-mediated downstream signalling during deterioration of oocyte quality in vitro. The use of various antioxidants against ROS and OS-mediated impairment of oocyte quality in vitro has also been explored in order to increase the success rate of IVF during assisted reproductive health management.

Impact of oxygen tension during in vitro maturation: a sibling-oocyte prospective double-blinded study

OBJECTIVE

To determine whether oxygen (O2) tension (20% vs. 5%) has an impact on oocyte maturation rates and morphology during in vitro maturation (IVM).

DESIGN

A prospective, observational, monocentric, sibling-oocyte study.

SETTING

University Hospital.

PATIENTS

A total of 143 patients who underwent IVM for fertility preservation purposes from November 2016 to April 2021 were analyzed. Patients were included when ≥2 cumulus-oocyte complexes (COCs) were retrieved. The cohort of COCs obtained for each patient was randomly split into two groups: group 20% O2 and group 5% O2.

INTERVENTION

Cumulus-oocyte complexes were incubated for 48 hours either under 5% O2 or 20% O2. After 24 and 48 hours of culture, every oocyte was assessed for maturity and morphology, to estimate oocyte quality. Morphology was evaluated considering six parameters (shape, size, ooplasm, perivitelline space, zona pellucida, and polar body characteristics), giving a total oocyte score ranging from -6 to +6.

MAIN OUTCOME MEASURES

Maturation rates and total oocyte scores were compared using paired-sample analysis between group 20% O2 and group 5% O2.

RESULTS

Patient median age was 31.4 [28.1-35.2] years-old. The mean serum antimüllerian hormone levels and antral follicle count were 3.2 ± 2.3 ng/mL and 27.2 ± 16.0 follicles, respectively. A mean of 10.7 COCs per cycle were retrieved, leading to 6.1 ± 2.4 metaphase II oocytes vitrified (total maturation rate = 57.3%; 991 metaphase II oocytes/1,728 COCs). A total of 864 COCs were included in each group. Oocyte maturation rates were not different between the two groups (group 20% O2: 56.82% vs. group 5% O2: 57.87%, respectively). Regarding oocyte morphology, the mean total oocyte score was significantly higher in group 5% O2 compared with group 20% O2 (3.44 ± 1.26 vs. 3.16 ± 1.32, P=.014).

CONCLUSION

As culture under low O2 tension (5% O2) improves oocyte morphology IVM, our results suggest that culture under hypoxia should be standardized. Additional studies are warranted to assess the impact of O2 tension on oocyte maturation and the benefit of IVM under low O2 tension for embryo culture after utilization of frozen material.

No major differences in perinatal and maternal outcomes between uninterrupted embryo culture in time-lapse system and conventional embryo culture

STUDY QUESTION

Is embryo culture in a closed time-lapse system associated with any differences in perinatal and maternal outcomes in comparison to conventional culture and spontaneous conception?

SUMMARY ANSWER

There were no significant differences between time-lapse and conventional embryo culture in preterm birth (PTB, <37 weeks), low birth weight (LBW, >2500 g) and hypertensive disorders of pregnancy for singleton deliveries, the primary outcomes of this study.

WHAT IS KNOWN ALREADY

Evidence from prospective trials evaluating the safety of time-lapse incubation for clinical use show similar embryo development rates, implantation rates, and ongoing pregnancy and live birth rates when compared to conventional incubation. Few studies have investigated if uninterrupted culture can alter risks of adverse perinatal outcomes presently associated with IVF when compared to conventional culture and spontaneous conceptions.

STUDY DESIGN, SIZE, DURATION

This study is a Swedish population-based retrospective registry study, including 7379 singleton deliveries after fresh embryo transfer between 2013 and 2018 from selected IVF clinics. Perinatal outcomes of singletons born from time-lapse-cultured embryos were compared to singletons from embryos cultured in conventional incubators and 71 300 singletons from spontaneous conceptions. Main perinatal outcomes included PTB and LBW. Main maternal outcomes included hypertensive disorders of pregnancy (pregnancy hypertension and preeclampsia).

PARTICIPANTS/MATERIALS, SETTING, METHODS

From nine IVF clinics, 2683 singletons born after fresh embryo transfer in a time-lapse system were compared to 4696 singletons born after culture in a conventional incubator and 71 300 singletons born after spontaneous conception matched for year of birth, parity, and maternal age. Patient and treatment characteristics from IVF deliveries were cross-linked with the Swedish Medical Birth Register, Register of Birth Defects, National Patient Register and Statistics Sweden. Children born after sperm and oocyte donation cycles and after Preimplantation Genetic testing cycles were excluded. Odds ratio (OR) and adjusted OR were calculated, adjusting for relevant confounders.

MAIN RESULTS AND THE ROLE OF CHANCE

In the adjusted analyses, no significant differences were found for risk of PTB (adjusted OR 1.11, 95% CI 0.87-1.41) and LBW (adjusted OR 0.86, 95% CI 0.66-1.14) or hypertensive disorders of pregnancy; preeclampsia and hypertension (adjusted OR 0.99, 95% CI 0.67-1.45 and adjusted OR 0.98, 95% CI 0.62-1.53, respectively) between time-lapse and conventional incubation systems. A significantly increased risk of PTB (adjusted OR 1.31, 95% CI 1.08-1.60) and LBW (adjusted OR 1.36, 95% CI 1.08-1.72) was found for singletons born after time-lapse incubation compared to singletons born after spontaneous conceptions. In addition, a lower risk for pregnancy hypertension (adjusted OR 0.72 95% CI 0.53-0.99) but no significant difference for preeclampsia (adjusted OR 0.87, 95% CI 0.68-1.12) was found compared to spontaneous conceptions. Subgroup analyses showed that some risks were related to the day of embryo transfer, with more adverse outcomes after blastocyst transfer in comparison to cleavage stage transfer.

LIMITATIONS, REASONS FOR CAUTION

This study is retrospective in design and different clinical strategies may have been used to select specific patient groups for time-lapse versus conventional incubation. The number of patients is limited and larger datasets are required to obtain more precise estimates and adjust for possible effect of additional embryo culture variables.

WIDER IMPLICATIONS OF THE FINDINGS

Embryo culture in time-lapse systems is not associated with major differences in perinatal and maternal outcomes, compared to conventional embryo culture, suggesting that this technology is an acceptable alternative for embryo incubation.

STUDY FUNDING/COMPETING INTEREST(S)

The study was financed by a research grant from Gedeon Richter. There are no conflicts of interest for all authors to declare.

TRIAL REGISTRATION NUMBER

N/A.

The destinies of human embryos reaching blastocyst stage between Day 4 and Day 7 diverge as early as fertilization

STUDY QUESTION

What clinical and laboratory differences emerge from parallel direct comparison of embryos reaching the blastocyst stage between Days 4, 5, 6, and 7 (Days 4-7)?

SUMMARY ANSWER

Increasing times to blastocyst formation are associated with a worse clinical outcome and perturbations in developmental patterns appear as early as the fertilization stage.

WHAT IS KNOWN ALREADY

Previous evidence indicates that later times to blastocyst development are associated with a worse clinical outcome. However, the vast majority of these data concern Day 5 and Day 6 blastocysts, while Day 4 and Day 7 blastocysts remain less thoroughly investigated. In addition, studies comparing in parallel the developmental patterns and trajectories of Day 4-7 blastocysts are lacking. This leaves unanswered the question of when and how differences among such embryos emerge. Acquisition of such knowledge would significantly contribute to understanding the relative impact of intrinsic and extrinsic causes of embryo developmental kinetics and competence.

STUDY DESIGN, SIZE, DURATION

This retrospective study involved time-lapse technology (TLT) monitoring of Day 4 (N = 70), Day 5 (N = 6147), Day 6 (N = 3243), and Day 7 (N = 149) blastocysts generated in 9450 ICSI cycles. Oocyte retrievals were carried out after clomiphene citrate-based minimal ovarian stimulation, between January 2020 and April 2021.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Couples included in the study presented with different diagnoses, mainly male factor and unexplained infertility. Cases involving cryopreserved gametes or surgically retrieved sperm were excluded. Microinjected oocytes were assessed by a combined TLT-culture system. Day 4-7 blastocyst groups were compared in terms of morphokinetics (pronuclear dynamics, cleavage patterns and timings, and embryo quality) and clinical outcome. Clinically usable blastocysts were cryopreserved and transferred in single vitrified-warmed blastocyst transfers (SVBT).

MAIN RESULTS AND THE ROLE OF CHANCE

From 19 846 microinjected oocytes, 17 144 zygotes (86.4%) were obtained. Overall, the blastocyst development rate was 56.0%. Rates of blastocysts formation on Days 4, 5, 6, and 7 were 0.7%, 64.0%, 33.8%, and 1.6%, respectively. The average expanded blastocyst development times were 98.4 ± 0.4, 112.4 ± 0.1, 131.6 ± 0.1, and 151.2 ± 0.5 h in the Day 4-7 groups, respectively. Female age was positively associated with longer times to blastocyst development. Rates of both inner cell mass (ICM) and trophectoderm (TE) morphological grade A blastocysts were negatively associated with the day of blastocyst development (P < 0.0001). The differences in development times and intervals increased progressively until blastocyst expansion (P < 0.0001 for all development times). Strikingly, such differences were already markedly evident as early as the time of pronuclear fading (tPNf) (20.6 ± 0.3, 22.5 ± 0.0, 24.0 ± 0.0, 25.5 ± 0.3; Days 4-7, respectively; P < 0.0001). Rates of cleavage anomalies (tri-/multi-chotomous mitosis or rapid cleavage) occurring at the first or second/third division cycles were also positively associated with longer times to blastocyst development. Implantation, ongoing pregnancy, and live birth rates were progressively reduced with increasing blastocyst development times (P < 0.0001), even after stratification for maternal age. When controlled for female age, male age, number of previous embryo transfer cycles, morphological grade of the ICM and TE, and progesterone supplementation, the probabilities of implantation, clinical, and ongoing pregnancy and live birth were significantly decreased in Day 6 blastocysts in comparison to Day 5 blastocysts. Follow-up data on birth length, weight, and malformations were comparable among the four blastocyst groups.

LIMITATIONS, REASONS FOR CAUTION

The study is limited by its retrospective design. Having been obtained from a single centre, the data require independent validation.

WIDER IMPLICATIONS OF THE FINDINGS

This study extends previous data on the relation between time of blastocyst formation and clinical outcome. It also indicates that differences in developmental times and patterns of Day 4-7 blastocysts occur as early as the fertilization stage, possibly dictated by intrinsic gamete-derived factors.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the participating institutions. The authors have no conflict of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Making and selecting the best embryo in the laboratory

Over the past 4 decades our ability to maintain a viable human embryo in vitro has improved dramatically, leading to higher implantation rates. This has led to a notable shift to single blastocyst transfer and the ensuing elimination of high order multiple gestations. Future improvements to embryo culture systems will not only come from new improved innovative media formulations (such as the inclusion of antioxidants), but plausibly by moving away from static culture to more dynamic perfusion-based systems now made a reality owing to the breakthroughs in three-dimensional printing technology and micro fabrication. Such an approach has already made it feasible to create high resolution devices for intracytoplasmic sperm injection, culture, and cryopreservation, paving the way not only for improvements in outcomes but also automation of assisted reproductive technology. Although improvements in culture systems can lead to further increases in pregnancy outcomes, the ability to quantitate biomarkers of embryo health and viability will reduce time to pregnancy and decrease pregnancy loss. Currently artificial intelligence is being used to assess embryo development through image analysis, but we predict its power will be realized through the creation of selection algorithms based on the integration of information related to metabolic functions, cell-free DNA, and morphokinetics, thereby using vast amounts of different data types obtained for each embryo to predict outcomes. All of this will not only make assisted reproductive technology more effective, but it will also make it more cost effective, thereby increasing patient access to infertility treatment worldwide.

Using Unlabeled Information of Embryo Siblings from the Same Cohort Cycle to Enhance In Vitro Fertilization Implantation Prediction

High-content time-lapse embryo imaging assessed by machine learning is revolutionizing the field of in vitro fertilization (IVF). However, the vast majority of IVF embryos are not transferred to the uterus, and these masses of embryos with unknown implantation outcomes are ignored in current efforts that aim to predict implantation. Here, whether, and to what extent the information encoded within "sibling" embryos from the same IVF cohort contributes to the performance of machine learning-based implantation prediction is explored. First, it is shown that the implantation outcome is correlated with attributes derived from the cohort siblings. Second, it is demonstrated that this unlabeled data boosts implantation prediction performance. Third, the cohort properties driving embryo prediction, especially those that rescued erroneous predictions, are characterized. The results suggest that predictive models for embryo implantation can benefit from the overlooked, widely available unlabeled data of sibling embryos by reducing the inherent noise of the individual transferred embryo.

Assessing the influence of distinct culture media on human pre-implantation development using single-embryo transcriptomics

The use of assisted reproductive technologies is consistently rising across the world. However, making an informed choice on which embryo culture medium should be preferred to ensure satisfactory pregnancy rates and the health of future children critically lacks scientific background. In particular, embryos within their first days of development are highly sensitive to their micro-environment, and it is unknown how their transcriptome adapts to different embryo culture compositions. Here, we determined the impact of culture media composition on gene expression in human pre-implantation embryos. By employing single-embryo RNA-sequencing after 2 or 5 days of the post-fertilization culture in different commercially available media (Ferticult, Global, and SSM), we revealed medium-specific differences in gene expression changes. Embryos cultured pre-compaction until day 2 in Ferticult or Global media notably displayed 266 differentially expressed genes, which were related to essential developmental pathways. Herein, 19 of them could have a key role in early development, based on their previously described dynamic expression changes across development. When embryos were cultured after day 2 in the same media considered more suitable because of its amino acid enrichment, 18 differentially expressed genes thought to be involved in the transition from early to later embryonic stages were identified. Overall, the differences were reduced at the blastocyst stage, highlighting the ability of embryos conceived in a suboptimal in vitro culture medium to mitigate the transcriptomic profile acquired under different pre-compaction environments.

Lineage segregation in human pre-implantation embryos is specified by YAP1 and TEAD1

STUDY QUESTION

Which processes and transcription factors specify the first and second lineage segregation events during human preimplantation development?

SUMMARY ANSWER

Differentiation into trophectoderm (TE) cells can be initiated independently of polarity; moreover, TEAD1 and YAP1 co-localize in (precursor) TE and primitive endoderm (PrE) cells, suggesting a role in both the first and the second lineage segregation events.

WHAT IS KNOWN ALREADY

We know that polarity, YAP1/GATA3 signalling and phospholipase C signalling play a key role in TE initiation in compacted human embryos, however, little is known about the TEAD family of transcription factors that become activated by YAP1 and, especially, whether they play a role during epiblast (EPI) and PrE formation. In mouse embryos, polarized outer cells show nuclear TEAD4/YAP1 activity that upregulates Cdx2 and Gata3 expression while inner cells exclude YAP1 which upregulates Sox2 expression. The second lineage segregation event in mouse embryos is orchestrated by FGF4/FGFR2 signalling which could not be confirmed in human embryos; TEAD1/YAP1 signalling also plays a role during the establishment of mouse EPI cells.

STUDY DESIGN, SIZE, DURATION

Based on morphology, we set up a development timeline of 188 human preimplantation embryos between Day 4 and 6 post-fertilization (dpf). The compaction process was divided into three subgroups: embryos at the start (C0), during (C1), and at the end (C2) of, compaction. Inner cells were identified as cells that were entirely separated from the perivitelline space and enclosed by cellular contacts on all sides. The blastulation process was divided into six subgroups, starting with early blastocysts with sickle-cell shaped outer cells (B0) and further on, blastocysts with a cavity (B1). Full blastocysts (B2) showed a visible ICM and outer cells referred to as TE. Further expanded blastocysts (B3) had accumulated fluid and started to expand due to TE cell proliferation and zona pellucida (ZP) thinning. The blastocysts then significantly expanded further (B4) and started to hatch out of the ZP (B5) until they were fully hatched (B6).

PARTICIPANTS/MATERIALS, SETTING, METHODS

After informed consent and the expiration of the 5-year cryopreservation duration, 188 vitrified high quality eight-cell stage human embryos (3 dpf) were warmed and cultured until the required stages were reached. We also cultured 14 embryos that were created for research until the four- and eight-cell stage. The embryos were scored according to their developmental stage (C0-B6) displaying morphological key differences, rather than defining them according to their chronological age. They were fixed and immunostained for different combinations of cytoskeleton (F-actin), polarization (p-ERM), TE (GATA3), EPI (NANOG), PrE (GATA4 and SOX17), and members of the Hippo signalling pathway (YAP1, TEAD1 and TEAD4). We choose these markers based on previous observations in mouse embryos and single cell RNA-sequencing data of human embryos. After confocal imaging (LSM800, Zeiss), we analysed cell numbers within each lineage, different co-localization patterns and nuclear enrichment.

MAIN RESULTS AND THE ROLE OF CHANCE

We found that in human preimplantation embryos compaction is a heterogeneous process that takes place between the eight-cell to the 16-cell stages. Inner and outer cells are established at the end of the compaction process (C2) when the embryos contain up to six inner cells. Full apical p-ERM polarity is present in all outer cells of compacted C2 embryos. Co-localization of p-ERM and F-actin increases steadily from 42.2% to 100% of the outer cells, between C2 and B1 stages, while p-ERM polarizes before F-actin (P < 0.00001). Next, we sought to determine which factors specify the first lineage segregation event. We found that 19.5% of the nuclei stain positive for YAP1 at the start of compaction (C0) which increases to 56.1% during compaction (C1). At the C2 stage, 84.6% of polarized outer cells display high levels of nuclear YAP1 while it is absent in 75% of non-polarized inner cells. In general, throughout the B0-B3 blastocyst stages, polarized outer/TE cells are mainly positive for YAP1 and non-polarized inner/ICM cells are negative for YAP1. From the C1 stage onwards, before polarity is established, the TE marker GATA3 is detectable in YAP1 positive cells (11.6%), indicating that differentiation into TE cells can be initiated independently of polarity. Co-localization of YAP1 and GATA3 increases steadily in outer/TE cells (21.8% in C2 up to 97.3% in B3). Transcription factor TEAD4 is ubiquitously present throughout preimplantation development from the compacted stage onwards (C2-B6). TEAD1 displays a distinct pattern that coincides with YAP1/GATA3 co-localization in the outer cells. Most outer/TE cells throughout the B0-B3 blastocyst stages are positive for TEAD1 and YAP1. However, TEAD1 proteins are also detected in most nuclei of the inner/ICM cells of the blastocysts from cavitation onwards, but at visibly lower levels as compared to that in TE cells. In the ICM of B3 blastocysts, we found one main population of cells with NANOG+/SOX17-/GATA4- nuclei (89.1%), but exceptionally we found NANOG+/SOX17+/GATA4+ cells (0.8%). In seven out of nine B3 blastocysts, nuclear NANOG was found in all the ICM cells, supporting the previously reported hypothesis that PrE cells arise from EPI cells. Finally, to determine which factors specify the second lineage segregation event, we co-stained for TEAD1, YAP1, and GATA4. We identified two main ICM cell populations in B4-6 blastocysts: the EPI (negative for the three markers, 46.5%) and the PrE (positive for the three markers, 28.1%) cells. We conclude that TEAD1 and YAP1 co-localise in (precursor) TE and PrE cells, indicating that TEAD1/YAP1 signalling plays a role in the first and the second lineage segregation events.

LIMITATIONS, REASONS FOR CAUTION

In this descriptive study, we did not perform functional studies to investigate the role of TEAD1/YAP1 signalling during the first and second lineage segregation events.

WIDER IMPLICATIONS OF THE FINDINGS

Our detailed roadmap on polarization, compaction, position and lineage segregation events during human preimplantation development paves the way for further functional studies. Understanding the gene regulatory networks and signalling pathways involved in early embryogenesis could ultimately provide insights into why embryonic development is sometimes impaired and facilitate the establishment of guidelines for good practice in the IVF lab.

STUDY FUNDING/COMPETING INTERESTS

This work was financially supported by Wetenschappelijk Fonds Willy Gepts (WFWG) of the University Hospital UZ Brussel (WFWG142) and the Fonds Wetenschappelijk Onderzoek-Vlaanderen (FWO, G034514N). M.R. is doctoral fellow at the FWO. The authors have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Development of a Microfluidic Chip Powered by EWOD for In Vitro Manipulation of Bovine Embryos

Digital microfluidics (DMF) holds great potential for the alleviation of laboratory procedures in assisted reproductive technologies (ARTs). The electrowetting on dielectric (EWOD) technology provides dynamic culture conditions in vitro that may better mimic the natural embryo microenvironment. Thus far, EWOD microdevices have been proposed for in vitro gamete and embryo handling in mice and for analyzing the human embryo secretome. This article presents the development of the first microfluidic chip utilizing EWOD technology designed for the manipulation of bovine embryos in vitro. The prototype sustains the cell cycles of embryos manipulated individually on the chips during in vitro culture (IVC). Challenges related to the chip fabrication as well as to its application during bovine embryo IVC in accordance with the adapted on-chip protocol are thoroughly discussed, and future directions for DMF in ARTs are indicated.

LHX6 promoter hypermethylation in oncological pediatric patients conceived by IVF

The multifactorial etiology of pediatric cancer is poorly understood. Environmental factors occurring during embryogenesis can disrupt epigenetic signaling, resulting in several diseases after birth, including cancer. Associations between assisted reproductive technologies (ART), such as in vitro fertilization (IVF), and birth defects, imprinting disorders and other perinatal adverse events have been reported. IVF can result in methylation changes in the offspring, and a link with pediatric cancer has been suggested. In this study, we investigated the peripheral blood methylomes of 11 patients conceived by IVF who developed cancer in childhood. Methylation data of patients and paired sex/aged controls were obtained using the Infinium MethylationEPIC Kit (Illumina). We identified 25 differentially methylated regions (DMRs), 17 of them hypermethylated, and 8 hypomethylated in patients. The most significant DMR was a hypermethylated genomic segment located in the promoter region of LHX6, a transcription factor involved in the forebrain development and interneuron migration during embryogenesis. An additional control group was included to verify the LHX6 methylation status in children with similar cancers who were not conceived by ART. The higher LHX6 methylation levels in IVF patients compared to both control groups (healthy children and children conceived naturally who developed similar pediatric cancers), suggested that hypermethylation at the LHX6 promoter could be due to the IVF process and not secondary to the cancer itself. Further studies are required to evaluate this association and the potential role of LHX6 promoter hypermethylation for tumorigenesis.

Timing of ICSI with Respect to Meiotic Spindle Status

The aim of this study was to evaluate the efficiency of using meiotic spindle (MS) visibility and relative position to the polar body (PB) as indicators of oocyte maturation in order to optimize intracytoplasmic sperm injection (ICSI) timing. This was a cohort study of patients younger than 40 years with planned ICSI, the timing of which was determined by MS status, compared with those without MS evaluation. The angle between PB and MS and MS visibility were evaluated by optical microscope with polarizing filter. Oocytes with MS evaluation were fertilized according to MS status either 5-6 h after ovum pick-up (OPU) or 7-8 h after OPU. Oocytes without MS evaluation were all fertilized 5-6 h after OPU. For patients over 35 years visualization of MS influenced pregnancy rate (PR): 182 patients with MS visualization had 32% PR (58/182); while 195 patients without MS visualization had 24% PR (47/195). For patients under 35 years, visualization of MS did not influence PR: 140 patients with MS visualization had 41% PR (58/140), while 162 patients without MS visualization had 41% PR (66/162). Visualization of MS therefore appears to be a useful parameter for assessment of oocyte maturity and ICSI timing for patients older than 35.

The effect of discrete wavelengths of visible light on the developing murine embryo

PURPOSE

A current focus of the IVF field is non-invasive imaging of the embryo to quantify developmental potential. Such approaches use varying wavelengths to gain maximum biological information. The impact of irradiating the developing embryo with discrete wavelengths of light is not fully understood. Here, we assess the impact of a range of wavelengths on the developing embryo.

METHODS

Murine preimplantation embryos were exposed daily to wavelengths within the blue, green, yellow, and red spectral bands and compared to an unexposed control group. Development to blastocyst, DNA damage, and cell number/allocation to blastocyst cell lineages were assessed. For the longer wavelengths (yellow and red), pregnancy/fetal outcomes and the abundance of intracellular lipid were investigated.

RESULTS

Significantly fewer embryos developed to the blastocyst stage when exposed to the yellow wavelength. Elevated DNA damage was observed within embryos exposed to blue, green, or red wavelengths. There was no effect on blastocyst cell number/lineage allocation for all wavelengths except red, where there was a significant decrease in total cell number. Pregnancy rate was significantly reduced when embryos were irradiated with the red wavelength. Weight at weaning was significantly higher when embryos were exposed to yellow or red wavelengths. Lipid abundance was significantly elevated following exposure to the yellow wavelength.

CONCLUSION

Our results demonstrate that the impact of light is wavelength-specific, with longer wavelengths also impacting the embryo. We also show that effects are energy-dependent. This data shows that damage is multifaceted and developmental rate alone may not fully reflect the impact of light exposure.

Effects of embryo density on cell number of day 3 embryos cultured in a 30-μl drop: a retrospective cohort study

For individual cultures, findings on regulating embryo density by changing the microdrop volume are contradictory. The aim of this study was to investigate the relationship between embryo density and the developmental outcome of day 3 embryos after adjusting covariates. In total, 1196 embryos from 206 couples who had undergone in vitro fertilization treatment were analyzed retrospectively. Three embryo densities were used routinely, i.e. one embryo in a drop (30 μl/embryo), two embryos in a drop (15 μl/embryo) and three embryos in a drop (10 μl/embryo). Embryo quality on day 3 was evaluated, both the cell number of day 3 embryos and the proportion of successful implantations served as endpoints. Maternal age, paternal age, antral follicles and level of anti-Müllerian hormone, type of infertility, controlled ovarian stimulation protocol, length of stimulation, number of retrieved oocytes, number of zygotes (two pronuclei) and insemination type were covariates and adjusted. After adjusting fully for all covariates, the cell number of day 3 embryos was significantly increased by 0.40 (95% CI 0.00, 0.79; P = 0.048) and 0.78 (95% CI 0.02, 1.54; P = 0.044) in the 15 μl/embryo and 10 μl/embryo group separately, compared with the 30 μl/embryo group. The proportions of implanted embryos were 42.1%, 48.7% and 0.0% in the 30 μl/embryo, 15 μl/embryo and 10 μl/embryo groups respectively. There was no statistical significance (P = 0.22) between the 30 μl/embryo group and the 15 μl/embryo group. After adjusting for confounders that were significant in univariate analysis, embryo density was still not associated with day 3 embryo implantation potential (P > 0.05). In a 30-μl microdrop, culturing embryos with an embryo density of both 15 and 10 μl/embryo increased the cell number of day 3 embryos, which did not benefit embryo implanting potential, compared with individual culture of 30 μl/embryo.

The Impact of Culture Medium on Morphokinetics of Cleavage Stage Embryos: An Observational Study

To study the impact of culture media on preimplantation morphokinetics used for predicting clinical outcomes. All IVF and ICSI cycles performed between 2012 and 2017 with time-lapse information available were included. In November 2014, culture medium was changed from Vitrolife G-1 PLUS to SAGE 1-Step. Each embryo was retrospectively assigned a morphokinetic-based KIDScore for prediction of implantation. Clinical outcomes were retrieved from medical records. Linear mixed models were used to study differences in morphokinetic parameters, a proportional odds model for KIDScore ranking and logistic regression for differences in clinical outcomes. All analyses were adjusted for patient and treatment characteristics. In 253 (63.1%) cycles, embryos (n = 671) were cultured in Vitrolife, and in 148 (36.9%) cycles, embryos (n = 517) were cultured in SAGE. All cleavage divisions occurred earlier for SAGE embryos than for Vitrolife embryos (2-cell: -2.28 (95%CI: -3.66, -0.89), 3-cell: -2.34 (95%CI: -4.00, -0.64), 4-cell: -2.41 (95%CI: -4.11, -0.71), 5-cell: -2.54 (95%CI: -4.90, -0.18), 6-cell: -3.58 (95%CI: -6.08, -1.08), 7-cell: -5.62 (95%CI: -8.80, -2.45) and 8-cell: -5.32 (95%CI: -9.21, -1.42) hours, respectively). Significantly more embryos cultured in SAGE classified for the highest KIDScore compared to embryos cultured in Vitrolife (p < 0.001). No differences were observed in clinical outcomes. Our results demonstrate an impact of culture medium on preimplantation embryo developmental kinetics, which affects classification within the KIDScore algorithm, while pregnancy outcomes were comparable between the groups. This study underscores the need to include the type of culture medium in the development of morphokinetic-based embryo selection tools.

Early programming of reproductive health and fertility: novel neuroendocrine mechanisms and implications in reproductive medicine

BACKGROUND

According to the Developmental Origins of Health and Disease (DOHaD) hypothesis, environmental changes taking place during early maturational periods may alter normal development and predispose to the occurrence of diverse pathologies later in life. Indeed, adverse conditions during these critical developmental windows of high plasticity have been reported to alter the offspring developmental trajectory, causing permanent functional and structural perturbations that in the long term may enhance disease susceptibility. However, while solid evidence has documented that fluctuations in environmental factors, ranging from nutrient availability to chemicals, in early developmental stages (including the peri-conceptional period) have discernible programming effects that increase vulnerability to develop metabolic perturbations, the impact and eventual mechanisms involved, of such developmental alterations on the reproductive phenotype of offspring have received less attention.

OBJECTIVE AND RATIONALE

This review will summarize recent advances in basic and clinical research that support the concept of DOHaD in the context of the impact of nutritional and hormonal perturbations, occurring during the periconceptional, fetal and early postnatal stages, on different aspects of reproductive function in both sexes. Special emphasis will be given to the effects of early nutritional stress on the timing of puberty and adult gonadotropic function, and to address the underlying neuroendocrine pathways, with particular attention to involvement of the Kiss1 system in these reproductive perturbations. The implications of such phenomena in terms of reproductive medicine will also be considered.

SEARCH METHODS

A comprehensive MEDLINE search, using PubMed as main interface, of research articles and reviews, published mainly between 2006 and 2021, has been carried out. Search was implemented using multiple terms, focusing on clinical and preclinical data from DOHaD studies, addressing periconceptional, gestational and perinatal programming of reproduction. Selected studies addressing early programming of metabolic function have also been considered, when relevant.

OUTCOMES

A solid body of evidence, from clinical and preclinical studies, has documented the impact of nutritional and hormonal fluctuations during the periconceptional, prenatal and early postnatal periods on pubertal maturation, as well as adult gonadotropic function and fertility. Furthermore, exposure to environmental chemicals, such as bisphenol A, and maternal stress has been shown to negatively influence pubertal development and gonadotropic function in adulthood. The underlying neuroendocrine pathways and mechanisms involved have been also addressed, mainly by preclinical studies, which have identified an, as yet incomplete, array of molecular and neurohormonal effectors. These include, prominently, epigenetic regulatory mechanisms and the hypothalamic Kiss1 system, which likely contribute to the generation of reproductive alterations in conditions of early nutritional and/or metabolic stress. In addition to the Kiss1 system, other major hypothalamic regulators of GnRH neurosecretion, such as γ-aminobutyric acid and glutamate, may be targets of developmental programming.

WIDER IMPLICATIONS

This review addresses an underdeveloped area of reproductive biology and medicine that may help to improve our understanding of human reproductive disorders and stresses the importance, and eventual pathogenic impact, of early determinants of puberty, adult reproductive function and fertility.

Deletion of Orc4 during oogenesis severely reduces polar body extrusion and blocks zygotic DNA replication†

Origin recognition complex subunit 4 (ORC4) is a DNA-binding protein required for DNA replication. During oocyte maturation, after the last oocyte DNA replication step and before zygotic DNA replication, the oocyte undergoes two meiotic cell divisions in which half the DNA is ejected in much smaller polar bodies. We previously demonstrated that ORC4 forms a cytoplasmic cage around the DNA that is ejected in both polar body extrusion (PBE) events. Here, we used ZP3 activated Cre to delete exon 7 of Orc4 during oogenesis to test how it affected both predicted functions of ORC4: its recently discovered role in PBE and its well-known role in DNA synthesis. Orc4 deletion severely reduced PBE. Almost half of Orc4-depleted germinal vesicle (GV) oocytes cultured in vitro were arrested before anaphase I (48%), and only 25% produced normal first polar bodies. This supports the role of ORC4 in PBE and suggests that transcription of the full-length Orc4 during oogenesis is required for efficient PBE. Orc4 deletion also abolished zygotic DNA synthesis. Fewer Orc4-depleted oocytes developed to the metaphase II (MII) stage, and after activation these oocytes were arrested at the two-cell stage without undergoing DNA synthesis. This confirms that transcription of full-length Orc4 after the primary follicle stage is required for zygotic DNA replication. The data also suggest that MII oocytes do not have a replication licensing checkpoint as cytokinesis progressed without DNA synthesis. Together, the data confirm that oocyte ORC4 is important for both PBE and zygotic DNA synthesis.

Use of mineral oil in IVF culture systems: physico-chemical aspects, management, and safety

PURPOSE

The study aims to summarize current knowledge on the use of oil in embryo culture systems, with a focus on proper management of different types of oil and possible impact on culture systems.

METHODS

PubMed was used to search the MEDLINE database for peer-reviewed English-language original articles and reviews concerning the use of oil in embryo culture systems. Searches were performed by adopting "embryo," "culture media," "oil," and "contaminants" as main terms. The most relevant publications were assessed and discussed critically.

RESULTS

Oils used in IVF are complex mixtures of straight-chain hydrocarbons, cyclic and aromatic hydrocarbons, and unsaturated hydrocarbons, whose precise composition influences their chemical and physical properties. Possible presence of contaminants suggests their storage at 4 °C in the dark to prevent peroxidation. Washing, generally performed by manufacturers prior to commercialization, may remove trace chemical contaminants. Oils reduce evaporation from culture media at rates depending on their chemical physical properties, culture system parameters, and incubator atmosphere. Contaminants - mainly metal ion and plastic components derived from refinement processes and storage - can pass to the aqueous phase of culture systems and affect embryo development.

CONCLUSIONS

Oils are essential components of culture systems. Their original quality and composition, storage, handling, and use can affect embryo development with significant efficiency and safety implications.

The effects of temperature variation treatments on embryonic development: a mouse study

Since the development of ART, embryos have been cultured at 37 °C in an attempt to mimic the in vivo conditions and the average body temperature of an adult. However, a gradient of temperatures within the reproductive tract has been demonstrated in humans and several other mammalian species. Therefore, the aim of this study was to evaluate the effects of temperature variation treatments on mouse embryo quality through morphokinetic events, blastocyst morphology, the relative gene expression of Igf2, Bax, Bcl2 and Apaf1 and the metabolomics of individual culture media. Study groups consisted of 2 circadian treatments, T1 with embryos being cultured at 37 °C during the day and 35.5 °C during the night, T2 with 38.5 °C during the day and 37 °C during the night and a control group with constant 37 °C. Our main findings are that the lower-temperature group (T1) showed a consistent negative effect on mouse embryo development with “slow” cleaving embryos, poor-quality blastocysts, a higher expression of the apoptotic gene Apaf1, and a significantly different set of amino acids representing a more stressed metabolism. On the other hand, our higher-temperature group (T2) showed similar results to the control group, with no adverse effects on blastocyst viability.

Cyclic fertilin-derived peptide stimulates in vitro human embryo development

OBJECTIVE

To study the cyclic fertilin peptide effects on preimplantation human embryogenesis. Cyclic fertilin peptide reproduces the structure of the binding site of the sperm Fertilin β (also named A Disintegrin and Metalloprotease 2: ADAM2) disintegrin domain. It binds to the oocyte membrane and increases sperm-oocyte fusion index in human and fertilization rate in mouse, providing healthy pups. It also improves human oocyte maturation and chromosome segregation in meiosis I and binds to human embryo blastomeres, suggesting that it has a membrane receptor.

DESIGN

Thawed human embryos at the 3 to 4 cells stage were randomly included in a dose-response study with cyclic fertilin peptide. Inner cell mass (ICM), trophectoderm (TE), and total cell numbers were evaluated in top- and good-quality blastocysts.

SETTING

The study was performed in an academic hospital and research laboratory.

PATIENT(S)

Human embryos donated for research. This project was approved by the French "Agence de la Biomédecine."

INTERVENTION(S)

Immunofluorescence and tissue-specific gene expression analysis, using Clariom D microarrays, were performed to study its mechanism of action.

MAIN OUTCOME MEASURE(S)

Cyclic fertilin peptide improves blastocyst formation by almost 20%, the concentration of 1 μM being the lowest most efficient concentration. It significantly increases twice the TE cell number, without modifying the ICM. It increases the in vitro hatching rate from 14% to 45%.

RESULT(S)

Cyclic fertilin peptide stimulates TE growth. In the ICM, it induces transcriptional activation of intracellular protein and vesicle-mediated transport.

CONCLUSION(S)

Cyclic fertilin peptide dramatically improves human embryo development potential. It could be used to supplement culture medium and improve the in vitro human embryo development. Starting supplementation immediately after fertilization, instead of day 2, could significantly upgrade assisted reproductive technology outcome.

Interplay of Oxidants and Antioxidants in Mammalian Embryo Culture System

One principal purpose of assisted reproductive technology (ART) is to produce viable and good quality embryos. However, a variety of environmental factors may induce epigenetic changes in the embryo. Moreover, laboratory conditions including the culture media may also affect embryo development. Therefore, media change is an important factor in maintaining proper oxidant/antioxidant balance during embryo culture. Alterations in the oxidant/antioxidant balance are related to various cellular responses such as an increase in the level of reactive oxygen species (ROS) and consequent lipid peroxidation (LPO), DNA damage, and apoptosis. The current study focuses on the role of external factors on embryo culture and the ability of antioxidants to enhance in vitro fertilization (IVF) outcomes. Indeed, an optimization of media culture by the addition of enzymatic and nonenzymatic antioxidants in animal models and human embryos in ART has been updated in this study, with an emphasis on comparing the available results and their possible reasons.

Biphasic (5-2%) oxygen concentration strategy significantly improves the usable blastocyst and cumulative live birth rates in in vitro fertilization

Oxygen (O₂) concentration is approximately 5% in the fallopian tube and 2% in the uterus in humans. A "back to nature" approach could increase in vitro fertilization (IVF) outcomes. This hypothesis was tested in this monocentric observational retrospective study that included 120 couples who underwent two IVF cycles between 2014 and 2019. Embryos were cultured at 5% from day 0 (D0) to D5/6 (monophasic O₂ concentration strategy) in the first IVF cycle, and at 5% O₂ from D0 to D3 and 2% O₂ from D3 to D5/6 (biphasic O₂ concentration strategy) in the second IVF cycle. The total and usable blastocyst rates (44.4% vs. 54.8%, p = 0.049 and 21.8% vs. 32.8%, p = 0.002, respectively) and the cumulative live birth rate (17.9% vs. 44.1%, p = 0.027) were significantly higher with the biphasic (5%-2%) O₂ concentration strategy. Whole transcriptome analysis of blastocysts donated for research identified 707 RNAs that were differentially expressed in function of the O₂ strategy (fold-change > 2, p value < 0.05). These genes are mainly involved in embryo development, DNA repair, embryonic stem cell pluripotency, and implantation potential. The biphasic (5-2%) O₂ concentration strategy for preimplantation embryo culture could increase the "take home baby rate", thus improving IVF cost-effectiveness and infertility management.

Impact of oxygen tension according to embryo stage of development: a prospective randomized study

Human embryo culture under 2-8% O2 is recommended by ESHRE revised guidelines for good practices in IVF labs. Nevertheless, notably due to the higher costs of embryo culture under hypoxia, some laboratories perform embryo culture under atmospheric O2 tension (around 20%). Furthermore, recent meta-analyses concluded with low evidence to a superiority of hypoxia on IVF/ICSI outcomes. Interestingly, a study on mice embryos suggested that oxidative stress (OS) might only have an adverse impact on embryos at cleavage stage. Hence, we aimed to demonstrate for the first time in human embryos that OS has a negative impact only at cleavage stage and that sequential culture conditions (5% O2 from Day 0 to Day 2/3, then «conventional» conditions at 20% O2 until blastocyst stage) might be a valuable option for human embryo culture. 773 IVF/ICSI cycles were included in this randomized clinical trial from January 2016 to April 2018. At Day 0 (D0), patients were randomized using a 1:2 allocation ratio between group A (20% O2; n = 265) and group B (5% O2; n = 508). Extended culture (EC) was performed when ≥ 5 Day 2-good-quality-embryos were available (n = 88 in group A (20% O2)). In subgroup B, 195 EC cycles were randomized again at Day 2 (using 1:1 ratio) into groups B' (5% O2 until Day 6 (n = 101)) or C (switch to 20% O2 from Day 2 to Day 6 (n = 94). Fertilization rate, cleavage-stage quality Day 2-top-quality-embryo (D2-TQE), blastocyst quality (Day 5-top-quality-blastocyst (D5-TQB) and implantation rate (IR) were compared between groups A and B (= cleavage-stage analysis), or A(20% O2), B'(5% O2) and C(5%-to-20% O2). Overall, characteristics were similar between groups A and B. Significantly higher rates of early-cleaved embryos, top-quality and good-quality embryos on Day 2 were obtained in group B compared to group A (P < 0.05). This association between oxygen tension and embryo quality at D2 was confirmed using an adjusted model (P < 0.05). Regarding blastocyst quality, culture under 20% O₂ from Day 0 to Day 6 (group A) resulted in significantly lower Day 5-TQB number and rates (P < 0.05) compared to both groups B' and C. Furthermore, blastocyst quality was statistically equivalent between groups B' and C (P = 0.45). At Day 6, TQB numbers and rates were also significantly higher in groups B' and C compared to group A (P < 0.05). These results were confirmed analyzing adjusted mean differences for number of Day 5 and Day 6 top quality embryos obtained in group A when compared to those respectively in groups B' and C (P < 0.05). No difference in clinical outcomes following blastocyst transfers was observed. These results would encourage to systematically culture embryos under hypoxia at least during early development stages, since OS might be detrimental exclusively before embryonic genome activation.

Soluble human leukocyte antigen-G is a potential embryo viability biomarker and a positive predictor of live-births in humans

PROBLEM

Human infertility affects 15-20% of reproductive-age couples and it is mitigated by assisted reproductive technology (ART) approaches. Poor biological viability of embryos contributes to implantation failure and live birth rate (LBR). This study is aimed to examine whether or not embryo-secreted soluble human leukocyte antigen-G (sHLA-G) is (i) associated with developing embryos and (ii) able to predict successful pregnancy outcome.

METHOD OF STUDY

A retrospective, multicentric study using 539 human embryo spent medium samples (E-SMs), analysed for sHLA-G levels by ELISA. Correlation analysis was performed on sHLA-G levels with developing embryonic stages, their quality scores and pregnancy outcome in terms of LBR.

RESULTS

Of 539 E-SMs analysed, 445 had detectable sHLA-G (83%) with levels varying within and across clinics and, between stages of embryonic development. Levels of sHLA-G (ng/mL) were significantly (P < .05) different in E-SMs of cleavage-stage embryos versus blastocysts. There was an insignificant correlation between the sHLA-G levels and morphology scores of embryos. But, sHLA-G levels showed a positive correlation with grades of blastocysts and importantly, its levels were significantly (P < .05) higher in live-birth vis-a-vis no-birth cases. Also, levels were higher in live-births out of blastocysts-ETs versus cleavage-stage-embryo transfers. Altered levels were observed with embryos, which resulted in miscarriages. Overall, a significant (P < .0001) association of sHLA-G with live births was observed.

CONCLUSION

Embryo-derived sHLA-G can be a valuable embryo viability, independent, biomarker, which can predict live-birth outcome and it could be useful as an adjunct to existing criteria for elective single embryo transfer.

Physicochemical and Functional Characterization of Female Reproductive Fluids: A Report of the First Two Infants Born Following Addition of Their Mother's Fluids to the Embryo Culture Media

Culture media supplemented with reproductive fluids (RF) have been used in livestock species, improving the efficiency and quality of in vitro produced embryos. However, usefulness in humans is still unknown. In this study, we collected human reproductive fluids (HRFs) ex vivo (from 25 patients undergoing abdominal hysterectomy plus bilateral salpingectomy) and in vivo (from 31 oocyte donors). Afterward, protocols to evaluate their osmolality, pH, total protein concentration, endotoxin level, and sterility were optimized, establishing security ranges for their use as natural additives. In addition, a functional assay was developed with bovine embryos grown in vitro in a medium supplemented with 1% of collected HRFs. Finally, a proof of concept was performed with six patients on post ovulation day 2 to evaluate the full-term viability of embryos grown in media supplemented with autologous uterine fluid, collected under in vivo conditions. Two of the embryos resulted in successful pregnancy and delivery of healthy babies. In conclusion, this study establishes a complete quality control sheet of HRFs as additives for embryo culture media and shows first preliminary data on obtaining healthy offspring derived from embryos grown in media supplemented with HRFs.

Different CO2 settings (6.0% vs 7.0%) do have an impact on extracellular pH of culture medium (pHe) and euploidy rates rather than on blastocyst development: a sibling oocyte study

OBJECTIVE

To determine whether euploidy rates and blastocyst development differ in a continuous culture medium under different CO₂ concentrations.

DESIGN AND METHOD

A single-center retrospective study was performed from July 2018 to October 2019 including 44 fresh cycles with at least four fresh mature oocytes (MII) without severe male factor infertility. Sibling MII were injected and cultured in Global®Total®LP under 6.0% (pHe = 7.374 ± 0.014) or 7.0% (pHe = 7.300 ± 0.013) CO₂, 5.0% O₂, and 89.0% or 88.0% N₂. Analyzed variables were normally fertilized oocytes (2PN), cleavage rate, blastulation rate on day 5/2PN, usable blastocyst (blastocysts biopsied/2PN), and euploidy rates. Blastocyst's trophectoderm biopsy was performed on day 5, 6, or 7 for genetic testing and mitochondrial DNA (mtDNA) quantification by next-generation sequencing.

RESULTS

Women's mean age was 33.0 ± 6.6 years old. From a total of 604 MII, no differences were found in normal fertilization and cleavage rates on day 3 between 6.0 and 7.0% CO₂ (72.3% vs 67.1%, p = 0.169 and 96.6% vs 96.3%, p = 0.897, respectively). Blastulation rate on day 5/2PN was comparable between 6.0 and 7.0% CO₂ (68.1% vs 64.2%, p = 0.409). Although usable blastocyst rate was not different (54.3% vs 55.3%, p = 0.922), total euploidy rates differed significantly (58.7% vs 42.8%, p = 0.016) between 6.0% and 7.0% CO₂, respectively. The mean blastocyst mtDNA content was significantly lower in 6.0% CO₂ (30.4 ± 9.1 vs 32.9 ± 10.3, p = 0.037).

CONCLUSION

Blastocyst development is not affected when embryos are cultured in vitro at 6.0% or 7.0% CO₂, while euploidy rates are significantly decreased at a higher CO₂ concentration, therefore at a lower pHe.

Metabolic activity of human blastocysts correlates with their morphokinetics, morphological grade, KIDScore and artificial intelligence ranking

STUDY QUESTION

Is there a relationship between blastocyst metabolism and biomarkers of embryo viability?

SUMMARY ANSWER

Blastocysts with higher developmental potential and a higher probability of resulting in a viable pregnancy consume higher levels of glucose and exhibit distinct amino acid profiles.

WHAT IS KNOWN ALREADY

Morphological and morphokinetic analyses utilized in embryo selection provide insight into developmental potential, but alone are unable to provide a direct measure of embryo physiology and inherent health. Glucose uptake is a physiological biomarker of viability and amino acid utilization is different between embryos of varying qualities.

STUDY DESIGN, SIZE, DURATION

Two hundred and nine human preimplantation embryos from 50 patients were cultured in a time-lapse incubator system in both freeze all and fresh transfer cycles. A retrospective analysis of morphokinetics, morphology (Gardner grade), KIDScore, artificial intelligence grade (EmbryoScore), glucose and amino acid metabolism, and clinical pregnancies was conducted.

PARTICIPANTS/MATERIALS, SETTING, METHODS

ICSI was conducted in all patients, who were aged ≤37 years and previously had no more than two IVF cycles. Embryos were individually cultured in a time-lapse incubator system, and those reaching the blastocyst stage had their morphokinetics annotated and were each assigned a Gardner grade, KIDScore and EmbryoScore. Glucose and amino acid metabolism were measured. Clinical pregnancies were confirmed by the presence of a fetal heartbeat at 6 weeks of gestation.

MAIN RESULTS AND THE ROLE OF CHANCE

Glucose consumption was at least 40% higher in blastocysts deemed of high developmental potential using either the Gardner grade (P < 0.01, n = 209), KIDScore (P < 0.05, n = 207) or EmbryoScore (P < 0.05, n = 184), compared to less viable blastocysts and in blastocysts that resulted in a clinical pregnancy compared to those that failed to implant (P < 0.05, n = 37). Additionally, duration of cavitation was inversely related to glucose consumption (P < 0.05, n = 200). Total amino acid consumption was significantly higher in blastocysts with an EmbryoScore higher than the cohort median score (P < 0.01, n = 185). Furthermore, the production of amino acids was significantly lower in blastocysts with a high Gardner grade (P < 0.05, n = 209), KIDScore (P < 0.05, n = 207) and EmbryoScore (P < 0.01, n = 184).

LIMITATIONS, REASONS FOR CAUTION

Samples were collected from patients who had ICSI treatment and from only one clinic.

WIDER IMPLICATIONS OF THE FINDINGS

These results confirm that metabolites, such as glucose and amino acids, are valid biomarkers of embryo viability and could therefore be used in conjunction with other systems to aid in the selection of a healthy embryo.

STUDY FUNDING/COMPETING INTEREST(S)

Work was supported by Virtus Health. D.K.G is contracted with Virtus Health. The other authors have no conflict of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Evolutionary consequences of environmental effects on gamete performance

Variation in pre- and post-release gamete environments can influence evolutionary processes by altering fertilization outcomes and offspring traits. It is now widely accepted that offspring inherit epigenetic information from both their mothers and fathers. Genetic and epigenetic alterations to eggs and sperm-acquired post-release may also persist post-fertilization with consequences for offspring developmental success and later-life fitness. In externally fertilizing species, gametes are directly exposed to anthropogenically induced environmental impacts including pollution, ocean acidification and climate change. When fertilization occurs within the female reproductive tract, although gametes are at least partially protected from external environmental variation, the selective environment is likely to vary among females. In both scenarios, gamete traits and selection on gametes can be influenced by environmental conditions such as temperature and pollution as well as intrinsic factors such as male and female reproductive fluids, which may be altered by changes in male and female health and physiology. Here, we highlight some of the pathways through which changes in gamete environments can affect fertilization dynamics, gamete interactions and ultimately offspring fitness. We hope that by drawing attention to this important yet often overlooked source of variation, we will inspire future research into the evolutionary implications of anthropogenic interference of gamete environments including the use of assisted reproductive technologies. This article is part of the theme issue 'How does epigenetics influence the course of evolution?'

Current Advancements in Noninvasive Profiling of the Embryo Culture Media Secretome

There have been over 8 million babies born through in vitro fertilization (IVF) and this number continues to grow. There is a global trend to perform elective single embryo transfers, avoiding risks associated with multiple pregnancies. It is therefore important to understand where current research of noninvasive testing for embryos stands, and what are the most promising techniques currently used. Furthermore, it is important to identify the potential to translate research and development into clinically applicable methods that ultimately improve live birth and reduce time to pregnancy. The current focus in the field of human reproductive medicine is to develop a more rapid, quantitative, and noninvasive test. Some of the most promising fields of research for noninvasive assays comprise cell-free DNA analysis, microscopy techniques coupled with artificial intelligence (AI) and omics analysis of the spent blastocyst media. High-throughput proteomics and metabolomics technologies are valuable tools for noninvasive embryo analysis. The biggest advantages of such technology are that it can differentiate between the embryos that appear morphologically identical and has the potential to identify the ploidy status noninvasively prior to transfer in a fresh cycle or before vitrification for a later frozen embryo transfer.

Design and Microfabrication of An On-Chip Oocyte Maturation System for Reduction of Apoptosis

Objective

In customary assisted reproductive technology (ART), oocyte culture occurs in static micro drops of Petri dishes with vast media volume; while, the in vivo condition is dynamic. In this study, we aimed to improve the maturation efficiency of mammalian oocytes by designing an optimal microchamber array to obtain the integration of oocyte trapping and maturation within a microfluidic device and evaluate the role of microfluidic culture condition in lipid peroxidation level of the culture medium, in vitro matured oocytes apoptosis, and its comparison with the conventional static system.

Materials and Methods

In this experimental research, immature oocytes were collected from ovaries of the Naval Medical Research Institute (NMRI) mice. Oocytes were randomly laid in static and dynamic (passive and active) in vitro maturation culture medium for 24 hours. The lipid peroxidation level in oocyte culture media was assessed by measuring the concentration of malondialdehyde (MDA), and the rate of apoptosis in in vitro matured oocytes was assessed by the TUNEL assay after a-24 hour maturation period.

Results

The MDA concentration in both dynamic oocyte maturation media were significantly lower than the static medium (0.003 and 0.002 vs. 0.13 μmol/L, P<0.01). Moreover, the rate of apoptosis in matured oocytes after a-24 hour maturation period was significantly lower in passive dynamic and active dynamic groups compared with the static group (16%, 15% vs. 35%, P<0.01).

Conclusion

The dynamic culture for in vitro oocyte maturation (IVM) improves the viability of IVM oocytes in comparison with the static culture condition.

Competence of embryos showing transient developmental arrest during in vitro culture

PURPOSE

In vitro developing embryos may apparently show no developmental progress during 24 h and resume their development up to the blastocyst stage. The present study was conducted to assess their ability to implant and to give rise to a live birth when replaced at day 5 (fresh or vitrified/warmed) as compared to continuously developing embryos.

METHODS

Embryo development follow-up and grade were prospectively recorded in a photo database. The studied period was from April 2011 to July 2017. The studied embryos included transient arrested embryos (TAE) that showed the same developmental stage at two subsequent observations, i.e. between day 2 and day 3 (d2 and d3), between day 3 and day 4 (d3 and d4) and between day 4 and day 5 (d4 and d5). TAE were compared to continuously developing embryos (CDE). Elective day 5 embryo transfers were performed.

RESULTS

Woman age was higher in TAE (34.3±3.9) than in CDE (32.9±4.8) (p<0.01). TAE were more frequently (63.1%) observed after ICSI than after conventional IVF (55.9%) (p<0.01). Implantation rate was reduced in TAE as compared to CDE, after both fresh (10.0% vs 23.8% [p<0.01]) and vitrified/warmed (12.9% vs 19.0% [p<0.01]) embryo transfers. Delivery rate was also lower after the transfer of fresh (8.3% vs 19.4% [p<0.01]) and vitrified/warmed (8.5% vs 14.1% [p<0.01]) TAE as compared to CDE. Implantation and delivery rates were not statistically different whether embryo arrested between day 2 and day 3 (d2 and d3), between day 3 and day 4 (d3 and d4) or between day 4 and day 5 (d4 and d5).

CONCLUSION

TAE may be considered for transfer at a lower priority than CDE and associated with inferior prognosis than CDE.

Small Noncoding RNA Signatures for Determining the Developmental Potential of an Embryo at the Morula Stage

As part of the optimization of assisted reproductive technology programs, the aim of the study was to identify key small noncoding RNA (sncRNA) molecules that participate in maternal-to-zygotic transition and determine development potential and competence to form a healthy fetus. Small RNA deep sequencing followed by quantitative real-time RT-PCR was used to profile sncRNAs in 50 samples of spent culture medium from morula with different development potentials (no potential (degradation/developmental arrest), low potential (poor-quality blastocyst), and high potential (good/excellent quality blastocyst capable of implanting and leading to live birth)) obtained from 27 subfertile couples who underwent in vitro fertilization. We have shown that the quality of embryos at the morula stage is determined by secretion/uptake rates of certain sets of piRNAs and miRNAs, namely hsa_piR_011291, hsa_piR_019122, hsa_piR_001311, hsa_piR_015026, hsa_piR_015462, hsa_piR_016735, hsa_piR_019675, hsa_piR_020381, hsa_piR_020485, hsa_piR_004880, hsa_piR_000807, hsa-let-7b-5p, and hsa-let-7i-5p. Predicted gene targets of these sncRNAs included those globally decreased at the 8-cell–morula–blastocyst stage and critical to early embryo development. We show new original data on sncRNA profiling in spent culture medium from morula with different development potential. Our findings provide a view of a more complex network that controls human embryogenesis at the pre-implantation stage. Further research is required using reporter analysis to experimentally confirm interactions between identified sncRNA/gene target pairs.

A combination of growth factors and cytokines alter preimplantation mouse embryo development, foetal development and gene expression profiles

Within the maternal tract, the preimplantation embryo is exposed to an array of growth factors (GFs) and cytokines, most of which are absent from culture media used in clinical IVF. Whilst the addition of individual GFs and cytokines to embryo culture media can improve preimplantation mouse embryo development, there is a lack of evidence on the combined synergistic effects of GFs and cytokines on embryo development and further foetal growth. Therefore, in this study, the effect of a combined group of GFs and cytokines on mouse preimplantation embryo development and subsequent foetal development and gene expression profiles was investigated. Supplementation of embryo culture media with an optimised combination of GFs and cytokines (0.05 ng/ml vascular endothelial GF, 1 ng/ml platelet-derived GF, 0.13 ng/ml insulin-like GF 1, 0.026 ng/ml insulin-like GF 2 and 1 ng/ml granulocyte colony-stimulating factor) had no effect on embryo morphokinetics but significantly increased trophectoderm cell number (P = 0.0002) and total cell number (P = 0.024). Treatment with this combination of GFs and cytokines also significantly increased blastocyst outgrowth area (P &lt; 0.05) and, following embryo transfer, increased foetal weight (P = 0.027), crown-rump length (P = 0.017) and overall morphological development (P = 0.027). RNA-seq analysis of in vitro derived foetuses identified concurrent alterations to the transcriptional profiles of liver and placental tissues compared with those developed in vivo, with greater changes observed in the GF and cytokine treated group. Together these data highlight the importance of balancing the actions of such factors for the regulation of normal development and emphasise the need for further studies investigating this prior to clinical implementation.

Understanding and Assisting Reproduction in Wildlife Species Using Microfluidics

Conservation breeding and assisted reproductive technologies (ARTs) are invaluable tools to save wild animal species that are on the brink of extinction. Microfluidic devices recently developed for human or domestic animal reproductive medicine could significantly help to increase knowledge about fertility and contribute to the success of ART in wildlife. Some of these microfluidic tools could be applied to wild species, but dedicated efforts will be necessary to meet specific needs in animal conservation; for example, they need to be cost-effective, applicable to multiple species, and field-friendly. Microfluidics represents only one powerful technology in a complex toolbox and must be integrated with other approaches to be impactful in managing wildlife reproduction.

Reducing time to pregnancy and facilitating the birth of healthy children through functional analysis of embryo physiology†

An ever-increasing number of couples rely on assisted reproductive technologies (ART) in order to conceive a child. Although advances in embryo culture have led to increases in the success rates of clinical ART, it often takes more than one treatment cycle to conceive a child. Ensuring patients conceive as soon as possible with a healthy embryo is a priority for reproductive medicine. Currently, selection of embryos for transfer relies predominantly on the morphological assessment of the preimplantation embryo; however, morphology is not an absolute link to embryo physiology, nor the health of the resulting child. Non-invasive quantitation of individual embryo physiology, a key regulator of both embryo viability and health, could provide valuable information to assist in the selection of the most viable embryo for transfer, hence reducing the time to pregnancy. Further, according to the Barker Hypothesis, the environment to which a fetus is exposed to during gestation affects subsequent offspring health. If the environment of the preimplantation period is capable of affecting metabolism, which in turn will affect gene expression through the metaboloepigenetic link, then assessment of embryo metabolism should represent an indirect measure of future offspring health. Previously, the term viable embryo has been used in association with the potential of an embryo to establish a pregnancy. Here, we propose the term healthy embryo to reflect the capacity of that embryo to lead to a healthy child and adult.

The role of honeybee pollen as a natural source of antioxidants in the in vitro maturation medium of sheep oocytes and its effect on gene expression

This study aimed to investigate the effect of honeybee pollen as an antioxidant source in a maturation medium of sheep oocytes on the in vitro maturation rate, glutathione concentration, and gene expression. To our knowledge, this study might be the first of its kind in this field. Sheep oocytes were cultured in vitro with honeybee pollen at four different concentrations (0.0, 1.0, 10.0, and 50.0 μg/ml). The results indicated that the ratio of oocytes that reached metaphase II stage was higher in the honeybee pollen-treated groups than in the control group (p ≤ 0.05). The reduced glutathione (GSH) mean content of matured oocytes was 9.85 nmol/25 oocytes, when honeybee pollen was added to the in vitro maturation (IVM) medium at a concentration of 1.0 μg/ml, compared with 5.84 and 4.44 nmol when using 10.0 and 50.0 μg/ml honeybee pollen, respectively. On the other hand, there was no significant difference in glutathione concentration between the control and 1.0 μg/ml honeybee pollen groups. Expression of candidate genes (GDF-9, BAX, Cyclin B, C-MOS, and IGF1) was upregulated in oocytes cultured with honeybee pollen when compared with oocytes cultured without honeybee pollen. In conclusion, the addition of honeybee pollen at a concentration of 1.0 μg/ml to IVM medium improved the in vitro maturation rate of sheep oocytes, increased the glutathione concentration, and improved gene expression.

How can we improve embryo production and pregnancy outcomes of Holstein embryos produced in vitro? (12 years of practical results at a California dairy farm)

Genomic evaluations have revolutionized dairy cattle breeding, and the demand for embryos produced from very young heifers with high genetic merit has increased over time. The combination of low oocyte recovery, young age of donors, and milk production status can make the in vitro embryo production (IVP) of Holstein cattle incredibly challenging. Several factors need to be coordinated to obtain a live calf from an IVP embryo, but the quality of the oocyte at the start of the process is one of the key factors. Aspects related to oocyte quality, laboratory quality control, embryo quality and recipient selection are addressed here, based on the measures that the RuAnn Genetics Laboratory (Riverdale, California, USA) adopted in the last 12 years, with the goal of improving production of live, healthy calves from Holstein embryos. Follicular wave synchronization and stimulation with follicular stimulating hormone (FSH) is necessary to improve oocyte quality and consequently embryo production. Laboratory quality control and the use of high-quality supplies are essential to reduce variability in production and facilitate identification of other factors that might interfere with embryo production. High pregnancy rates can be achieved with good quality embryos selected at optimal time and stage of development, transferred by an experienced embryo transfer (ET) technician, to well managed recipients 7 or 8 days after estrus. Attention to detail at every step of the process is crucial to success.

Effects of Supplementation with Natural Antioxidants on Oocytes and Preimplantation Embryos

For most infertile couples, in vitro fertilization (IVF) represents the only chance to conceive. Given the limited success of IVF procedures, novel approaches are continuously tested with the aim of improving IVF outcomes. Growing attention is devoted today to the potential benefit of natural antioxidants in the optimization of infertility treatments. This review summarizes current data in this context, focusing on both experimental studies on oocytes/embryos and clinical trials on antioxidants supplementation. Based on information gained from experimental studies, antioxidant supplementation may have beneficial effects on IVF outcomes in terms of quality and cryotolerance of in vitro produced embryos, together with positive effects on in vitro maturation oocytes and on early embryonic development. Unfortunately, from the clinical side, there is a paucity of evidence favoring the protective qualities of antioxidants. Among the antioxidants considered, coenzyme Q10 may be regarded as one of the most promising for its positive role in rescuing the oxidative stress-induced damages, but further data are needed. It is concluded that further trials are necessary to characterize the potential clinical value of antioxidants in IVF treatments.

Association between outdoor air pollution during in vitro culture and the outcomes of frozen-thawed embryo transfer

STUDY QUESTION

Does outdoor air pollution differentially affect the outcomes of frozen-thawed embryo transfer (FET) and fresh transfer in IVF treatment?

SUMMARY ANSWER

Increased SO2 and O3 levels at the site of IVF unit were significantly associated with lower live birth rates following FET but did not affect the contemporary fresh transfer outcomes.

WHAT IS KNOWN ALREADY

Ambient air pollution has been associated with human infertility and IVF outcomes. However, most of the studies excluded FET cycles.

STUDY DESIGN, SIZE, DURATION

A retrospective cohort study of 11148 patients contributing to 16290 transfer cycles between January 2013 and December 2016 was carried out.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The average age of the cohort was 31.51 ± 4.48 years and the average BMI was 21.14 ± 2.37 kg/cm2. Inverse distance weighting interpolation was used to estimate the daily ambient exposures to six pollutants (PM2.5, PM10, SO2, NO2, CO, O3) at an IVF clinical site, according to the data from fixed air quality monitoring stations in the city. The exposures of each cycle were presented as average daily concentrations of pollutants from oocyte retrieval to embryo transfer/cryopreservation. Exposures were analyzed in quartiles. A generalized estimating equation was used to evaluate the association between pollutants and IVF outcomes, adjusted for important confounding factors including maternal age, infertility diagnosis, BMI, endometrial status and embryo transfer policy.

MAIN RESULTS AND THE ROLE OF CHANCE

The clinical pregnancy rate and live birth rate of the cycles was 55.1% (8981/16290) and 47.1% (7672/16290), respectively. Among the included cycles, 4013 patients received 5299 FET cycles, resulting in 2263 live births (42.7% per ET), whereas 9553 patients received 10991 fresh transfer cycles, resulting in 5409 live births (49.2% per ET). SO2 and O3 levels were significantly associated with live birth rates in FET cycles, whereas none of the pollutants were significantly associated with IVF outcomes in contemporary fresh transfer cycles. The FET cycles in the highest quartile of SO2 and O3 exposure had significantly lower live birth rates (adjusted odds ratio (OR) 0.63, 95%CI 0.53-0.74; 0.69, 95% CI 0.58-0.82, respectively) in comparison with those in the lowest quartile. Models involving all transfer cycles and interaction terms (FET×exposures) suggested that FET significantly enhanced the effects of SO2 and O3 exposure on IVF outcomes (P < 0.001). Multi-pollutant models gave consistent results for the association between SO2 and live birth in FET cycles. Accounting for all six pollutants, women in the highest quartile of SO2 still had the lowest live birth rates (OR 0.61, 95%CI 0.47-0.80).

LIMITATIONS, REASONS FOR CAUTION

The study was limited by its retrospective nature. The exposure data were estimated according to monitoring data rather than measured directly from the IVF unit. Unknown confounding factors may skew the results.

WIDER IMPLICATIONS OF THE FINDINGS

Our data implied that embryos undergoing FET may be more vulnerable to a suboptimal environment than those undergoing fresh transfer. In heavily polluted sites or seasons, fluctuation in FET outcomes may be partially explained by the dynamic changes of ambient gaseous air pollutant.

STUDY FUNDING/COMPETING INTEREST(S)

National Natural Science Foundation (81302454). The authors have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.