Reducing the time of co-incubation of gametes in human in-vitro fertilization has no beneficial effects

Brief and long co-incubation of sperm and oocytes for in vitro fertilization: a meta-analysis of randomized controlled trials

Background

There is still no consensus on the optimal time of oocyte–sperm co-incubation during in vitro fertilization and embryo transfer (IVF-ET). The aim of this meta-analysis was to compare the effects of brief (1-6 h) and long (16-24 h) gametes co-incubation time on IVF outcomes.

Methods

The study protocol was registered online through PROSPERO (CRD42022337503) and PRISMA guidelines were followed in the present study. The following databases were searched from inception to May 2022 for randomized controlled trials (RCTs): PubMed, Embase, Cochrane library, Web of Science, using search terms related to IVF, gametes, time of co-incubation and reproductive outcome measure. Studies comparing outcomes of brief co-incubation to that of long co-incubation during IVF, and reporting primary outcome (live birth rate), secondary outcomes (clinical pregnancy rate; ongoing pregnancy rate; miscarriage rate; normal fertilization rate; polyspermy rate; top-quality embryo rate; implantation rate) were searched. A total of 11 studies were included in the meta-analysis. Combined odds ratio (OR) and 95% confidence interval (CI) were calculated for the data. Statistical heterogeneity analysis between studies was assessed by Cochran Q and I² statistic with a significant threshold of P < 0.05. Methodologic quality assessment of RCTs was made for potential risk of bias with Cochrane Risk of Bias Tool.

Results

Compared to long-term co-incubation, brief co-incubation had an advantage in increasing implantation rate (OR: 1.97, 95% CI: 1.52–2.57), ongoing pregnancy rate (OR: 2.18, 95% CI: 1.44–3.29) and top-quality embryo rate (OR: 1.17, 95% CI: 1.02–1.35). However, brief co-incubation of gametes had no advantages in the live-birth rate (OR: 1.09, 95% CI: 0.72–1.65), miscarriage rate (OR: 1.32, 95% CI: 0.55–3.18), clinical pregnancy rate (OR: 1.36, 95% CI: 0.99–1.87) and polyspermy rate (OR: 0.80, 95% CI: 0.48–1.33) than long-term co-incubation. Additionally, the brief co-incubation was associated with lower normal fertilization rate (OR: 0.89, 95% CI: 0.80–0.99), compared with long co-incubation.

Conclusions

Brief co-incubation of gametes had the advantages in increasing implantation rate, ongoing pregnancy rate and top-quality embryo rate than long-term co-incubation. However, the live-birth rate displayed no difference between the two in vitro fertilization methods. Gametes co-incubation time should be individualized according to each patient’s IVF history, infertility causes and the semen parameters.

Opportunities and Limits of Conventional IVF versus ICSI: It Is Time to Come off the Fence

Conventional IVF (c-IVF) is one of the most practiced assisted reproductive technology (ART) approaches used worldwide. However, in the last years, the number of c-IVF procedures has dropped dramatically in favor of intracytoplasmic sperm injection (ICSI) in cases of non-male-related infertility. In this review, we have outlined advantages and disadvantages associated with c-IVF, highlighting the essential steps governing its success, its limitations, the methodology differences among laboratories and the technical progress. In addition, we have debated recent insights into fundamental questions, including indications regarding maternal age, decreased ovarian reserve, endometriosis, autoimmunity, single oocyte retrieval-cases as well as preimplantation genetic testing cycles. The “overuse” of ICSI procedures in several clinical situations of ART has been critically discussed. These insights will provide a framework for a better understanding of opportunities associated with human c-IVF and for best practice guidelines applicability in the reproductive medicine field.

Effect Analysis of Degranulated Cell in Early Fertilization on FET Outcome and Offspring Safety with Data Mining

In vitro fertilization and embryo transfer is one type of assisted reproductive technology, although the technology is now more mature. Many factors, however, will have an impact on oocyte fertilization, embryo growth, pregnancy outcome, and child safety due to the journey from clinical to the laboratory. The influence of degranulated cells early in fertilization on frozen embryo transfer (FET) results is investigated in this study. This article analyzes 255 patients who underwent in vitro fertilization (IVF) and FET transplantation at the author's central unit from January 1, 2015, to June 30, 2021. Among them, IVF-assisted conception is the early degranulation of homologous oocyte fertilization. Correlation analysis is performed by observing the embryonic outcome of the early degranulation group and the overnight fertilization group and the clinical outcome after FET. Through data mining analysis, the results show that the polyfertilization rate and 0PN rate for the early degranulation group are significantly higher than the overnight fertilization group (9.87% vs. 8.24% and 3.14% vs. 1.69%). In terms of normal fertilization rate, there is no significant difference between D3 high-quality embryo rate and D5 high-quality blastocyst rate (64.07% vs. 65.15%, 27.5% vs. 26.5%, and 15.97% vs. 17.35%). There is no significant difference in the complete recovery rate of embryos after thawing (93.24% vs. 93.46%), and the implantation rate, clinical pregnancy rate, abortion rate, and live birth rate are not significantly different between the two groups after FET. The offspring outcomes of singletons do not differ significantly between the two groups; however, twins born early degranulate have much greater rates of ultralow birth weight and ultrapreterm children than twins born overnight fertilization (14.29% vs. 0). Therefore, it can be concluded that degranulation of cells early in fertilization is a desirable method to prevent fertilization disorders. However, under the premise of ensuring that no fertilization disorder occurs, it is not appropriate to degranulate all the oocytes of the patient at the early stage of fertilization.

Fertilization and neonatal outcomes after early rescue intracytoplasmic sperm injection: a retrospective analysis of 16,769 patients

Purpose

To evaluate the efficacy and safety of short-term insemination and early-rescue intracytoplasmic sperm injection (ICSI), an approach that rescued oocytes with unclear second polar body 6 h after initial insemination by ICSI (early R-ICSI) to avoid total or near-total fertilization failure in conventional in vitro fertilization (IVF).

Methods

We performed a retrospective study in 16,769 patients (short-term IVF, n = 12,094; ICSI, n = 3452; early R-ICSI, n = 1223) who received IVF/ICSI treatment in our hospital from January 2009 to October 2018. Fertilization and clinical outcomes were compared among those three groups.

Results

When considering the R-ICSI embryos in the early R-ICSI group independently, the rates of fertilization and day-3 cleaved embryos in 2PN oocytes were comparable, the rates of fertilization (2PN) and high-quality embryos were lower, whereas the multi-PN fertilization rate (3.27%) was significantly higher than the ICSI group (1.26%). The difference of clinical pregnancy rate between the part of transferred R-ICSI embryos (40.81%) and the ICSI group (44.73%) remained nonsignificant. Furthermore, the rate of congenital birth defects in the early R-ICSI group (0.99%) was not significantly different from those in the short-term IVF (0.76%) and ICSI groups (1.07%).

Conclusion

Despite the multi-PN fertilization rate, our study highlights early R-ICSI as a safe and effective alternative in assisted reproduction to decrease complete IVF fertilization failure and reduce ICSI utilization. Additional large amount and long-term follow-up studies are needed to further validate the use of early R-ICSI.

Comparison of embryonic competence and clinical outcomes between early and late cumulus cell removal for in vitro fertilization

Objective

The impact of early mechanical removal of cumulus cells on fertilization and embryonic development is not yet precisely known. This study aimed to investigate the effects of early and late cumulus cell removal on fertilization, polyspermy, embryonic development potential, blastocyst development, and clinical outcomes.

Methods

A prospective study was conducted of patients who underwent in vitro fertilization between September 2019 and October 2020. Sibling oocytes were randomly allocated after insemination to early cumulus cell removal at 6 hours (group I) and late cumulus cell removal at 16–18 hours (group II). If total fertilization failure (TFF) was determined to have occurred at early cumulus cell removal, rescue intracytoplasmic sperm injection (ICSI) was performed. Fertilization, embryonic development, and pregnancy outcomes were compared.

Results

A total of 912 oocytes were assigned to group I (458 oocytes) and group II (454 oocytes). Fertilization, polyspermy, embryo quality, and pregnancy outcomes were not significantly different between both groups. Rescue ICSI enabled fertilization of 79.2% of the TFF oocytes.

Conclusion

Early cumulus cell removal at 6 hours had no significant difference in fertilization, polyspermy, embryo development, or obstetric and perinatal outcomes compared to late removal. Early cumulus cell removal combined with early rescue ICSI may have the potential to help couples with TFF.

Controlled spermatozoa-oocyte interaction improves embryo quality in sheep

The current protocols of in vitro fertilization and culture in sheep rely on paradigms established more than 25 years ago, where Metaphase II oocytes are co-incubated with capacitated spermatozoa overnight. While this approach maximizes the number of fertilized oocytes, on the other side it exposes them to high concentration of reactive oxygen species (ROS) generated by active and degenerating spermatozoa, and positively correlates with polyspermy. Here we set up to precisely define the time frame during which spermatozoa effectively penetrates and fertilizes the oocyte, in order to drastically reduce spermatozoa-oocyte interaction. To do that, in vitro matured sheep oocytes co-incubated with spermatozoa in IVF medium were sampled every 30 min (start of incubation time 0) to verify the presence of a fertilizing spermatozoon. Having defined the fertilization time frame (4 h, data from 105 oocytes), we next compared the standard IVF procedures overnight (about 16 h spermatozoa/oocyte exposure, group o/nIVF) with a short one (4 h, group shIVF). A lower polyspermic fertilization (> 2PN) was detected in shIVF (6.5%) compared to o/nIVF (17.8%), P < 0.05. The o/nIVF group resulted in a significantly lower 2-cell stage embryos, than shIVF [34.6% (81/234) vs 50.6% (122/241) respectively, P < 0.001]. Likewise, the development to blastocyst stage confirmed a better quality [29% (70/241) vs 23.5% (55/234), shIVF vs o/nIVF respectively] and an increased Total Cell Number (TCN) in shIVF embryos, compared with o/n ones. The data on ROS have confirmed that its generation is IVF time-dependent, with high levels in the o/nIVF group. Overall, the data suggest that a shorter oocyte-spermatozoa incubation results in an improved embryo production and a better embryo quality, very likely as a consequence of a shorter exposure to the free oxygen radicals and the ensuing oxidative stress imposed by overnight culture.

Effects of Early Cumulus Cell Removal on Treatment Outcomes in Patients Undergoing In Vitro Fertilization: A Retrospective Cohort Study

BACKGROUND

Early cumulus cell removal combined with early rescue intracytoplasmic sperm injection (ICSI) has been widely practiced in many in vitro fertilization (IVF) centers in China in order to avoid total fertilization failure. However, uncertainty remains whether the pregnancy and neonatal outcomes are associated with early cumulus cell removal.

OBJECTIVES

To investigate if early cumulus cell removal alone after 4 hours co-incubation of gametes (4 h group), has detrimental effect on the pregnancy and neonatal outcomes in patients undergoing IVF, through a comparison with conventional cumulus cell removal after 20 hours of insemination (20 h group).

METHODS

This retrospective cohort study included 1784 patients who underwent their first fresh cleavage stage embryo transfer at the Centre for Assisted Reproduction of Shanghai First Maternity and Infant Hospital from June 2016 to December 2018 (4 h group, n=570; 20 h group, n=1214). A logistic regression analysis was performed to examine the independent association between early cumulus cell removal and pregnancy outcomes after adjustment for potential confounders. The neonatal outcomes between the two groups were compared.

RESULTS

When compared with the 20 h group, the 4 h group had similar pregnancy outcomes, including rates for biochemical pregnancy, clinical pregnancy, ongoing pregnancy, miscarriage, ectopic pregnancy, multiple pregnancy, live birth. There were 1073 infants delivered after embryo transfer (4 h group, n=337; 20 h group, n=736). Outcomes in both groups were similar for both singleton and twin gestations, including preterm birth rate and very preterm birth rate, mean birth weight, mean gestational age, sex ratio at birth and rate of congenital birth defects. In addition, findings pertaining to singleton gestations were also similar in the two groups for Z-scores (gestational age- and sex-adjusted birth weight), rates of small for gestational age, very small for gestational age, large for gestational age and very large for gestational age infants.

CONCLUSIONS

In this study early cumulus cell removal alone was not associated with adverse pregnancy and neonatal outcomes. From this perspective, early cumulus cell removal to assess for a potential early rescue ICSI is therefore considered to be a safe option in patients undergoing IVF.

A randomized triple blind controlled trial comparing the live birth rate of IVF following brief incubation versus standard incubation of gametes

STUDY QUESTION

Does brief incubation of oocytes and spermatozoa improve the live birth rate (LBR) of IVF when compared with that of standard incubation?

SUMMARY ANSWER

Brief incubation of gametes does not improve the LBR of IVF when compared with standard incubation.

WHAT IS KNOWN ALREADY

Some small randomized studies showed that brief incubation was associated with a significantly higher ongoing pregnancy rate than standard incubation.

STUDY DESIGN, SIZE, DURATION

This is a randomized triple blind study of 320 infertile women for their first or repeated cycles undergoing IVF between September 2015 and October 2016.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Women were randomized into the brief incubation group (n = 160) or the standard incubation group (n = 160) according to a computer-generated randomization list. Oocytes were incubated with spermatozoa (0.3-1.2 million motile sperm/ml) for 3-4 h in the brief incubation group while oocytes were incubated with spermatozoa at similar concentration for 20 h in the standard incubation group. The primary outcome was the LBR (a baby born alive after 22 weeks gestation) in the fresh cycle.

MAIN RESULTS AND THE ROLE OF CHANCE

There was no significant difference in the LBR between the brief and standard incubation groups based on both intention-to-treat [33.0% (53/160) versus 36.8% (59/160), relative risk (RR) 0.898 (95% CI = 0.666-1.212), P = 0.482] and per protocol [41.4%(53/128) versus 41.0% (59/144), RR1.011 (95% CI = 0.760-1.343), P = 0.942] analyses. Clinical pregnancy, ongoing pregnancy, miscarriage, multiple pregnancy and implantation rates were comparable for the two groups. Similar results were found with subgroup analysis of advanced maternal age, abnormal semen analysis and repeated IVF cycles. No differences were observed in cumulative LBR between two groups.

LIMITATIONS, REASONS FOR CAUTION

Various motile sperm concentrations of 0.3-1.2 million per ml were used for insemination and the reactive oxygen species level in the insemination medium was not measured. The highest level at 1.2 million per ml is still relatively low compared to prior studies, therefore we do not know whether brief incubation can improve the LBR using higher concentrations of spermatozoa. The present sample size may not be adequate to detect a smaller difference in the LBR.

WIDER IMPLICATIONS OF THE FINDINGS

The present study demonstrated that a brief incubation of gametes had no significant beneficial effect on the LBR when compared with the standard incubation. The practice of brief incubation of gametes is not necessary and this can save the already tight manpower in many laboratories.

STUDY FUNDING/COMPETING INTERESTS

The study was supported by the Merck-Serono China Research Fund for Fertility Experts (2015), which was not involved in study design, execution, data analysis and manuscript preparation. There are no conflicts of interest for all authors.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov Identifier NCT02534857.

TRIAL REGISTRATION DATE

28 August 2015.

DATE OF FIRST PATIENT’S ENROLMENT

8 September 2015.

Effect of early cumulus cells removal and early rescue ICSI on pregnancy outcomes in high-risk patients of fertilization failure

OBJECTIVE

The objective of this retrospective study was to evaluate clinical outcomes of early cumulus cells removal and early rescue intracytoplasmic sperm injection (ICSI) in high-risk patients of fertilization failure during human in vitro fertilization (IVF).

METHODS

A total of 5,518 patients were enrolled between January 2014 to December 2016. Of which 505 couples performed short insemination with >30% fertilization rate were included in short-term IVF group, 102 patients detected total fertilization failure (TFF) were treated with early rescue ICSI (R-ICSI group), and 4911 couples underwent conventional IVF with overnight co-incubation of gametes (traditional IVF group). The clinical outcomes were analyzed among the three groups.

RESULTS

The embryo implantation rates (40.34%, 39.78% and 42.42% for traditional, short-term IVF and R-ICSI groups, respectively) were comparable in the three groups. The clinical pregnancy rates among traditional IVF group, short-term IVF group and R-ICSI group were 57.95%, 57.03% and 60.78%, respectively, and the difference among three groups didn't reach significance.

CONCLUSION

The present study indicated that short insemination had no detrimental effects on clinical outcomes in human IVF and could prevent the occurrence of TFF combined with early rescue ICSI for high-risk patients of fertilization failure, which attained acceptable pregnancy outcomes.

Long-time vs. short-time insemination of sibling eggs

This study aimed to evaluate the impact of a short insemination procedure on embryo development, assess the reliability of a fertilization check prior to the appearance of pronuclei and elucidate the role of rescue intracytoplasmic sperm injection (R-ICSI). Patients who had ≥9 eggs, were aged <38 years and had normal semen samples were included. The sibling eggs of each patient were divided into two groups; one half for conventional in vitro fertilization (IVF; insemination time, 20 h) and the other half for short insemination (insemination time, 5 h). R-ICSI was performed where total fertilization failure (TFF) was deemed to have occurred in the short insemination group. In total, 2,465 eggs were included. No significant differences were found in fertilization, abnormal fertilization, embryo quality, clinical pregnancy and implantation rates between the short insemination and conventional insemination groups. In the short insemination group, R-ICSI was performed in 11 cycles (6.7%); in 6 of these cycles, fertilization occurred in the patient's eggs in the 20 h insemination group, while in the other 5 cycles, the patient's eggs were not fertilized after 20 h insemination either. Following R-ICSI, 19 of 36 eggs were normally fertilized. Subsequently, 7 embryos were transferred in 4 fresh cycles resulting in one ectopic pregnancy. In conclusion, the short insemination procedure does not improve embryo development and pregnancy rates. Short insemination combined with early R-ICSI may be a method of preventing total fertilization failure, albeit with poor accuracy.

Does reducing gamete co-incubation time improve clinical outcomes: a retrospective study

PURPOSE

The objective of this retrospective study was to determine whether patients undergoing in vitro fertilization (IVF) benefit from reducing the gamete co-incubation time.

METHODS

Patients (n = 570) were enrolled, including 281 patients in the reduced incubation time group (2-h incubation) and 289 patients in the standard IVF group (18-h incubation).

RESULTS

The observed outcomes, including the clinical pregnancy rate (CPR), implantation rate (IR), live birth rate (LBR), and miscarriage rate (MR), were similar between the two groups. When the data were divided into two subgroups based on the maternal age (≤30 and >30 years), the rates of top-quality embryos (30.83 vs. 25.89 %; p = 0.028), CPR (66.67 vs. 42.11 %; p = 0.013), and IR (41.90 vs. 31.25 %, p = 0.019) of the 2-h incubation group were significantly higher in the younger subgroup. However, for older patients, only a lower MR (7.59 vs. 20.83 %; p = 0.019) was achieved. Reducing the time of incubation still improved the CPR (OR = 1.993, 95 % CI 1.141-3.480) and MR (OR = 3.173, 95 % CI 1.013-9.936) in the younger and older subgroups, respectively, after it was adjusted for potential confounders.

CONCLUSIONS

Reducing incubation time improves the clinical results of IVF, although the LBR is not statistically different between the 2- and 18-h incubation time groups. And the specific clinical outcomes of reducing incubation time varied between the >30-year-old and the ≤30-year-old.

Brief co-incubation of sperm and oocytes for in vitro fertilization techniques

BACKGROUND

The in vitro fertilization (IVF) technique is commonly used and is the only treatment option for a proportion of infertile couples. To obtain better outcomes of IVF, it is important to enhance embryo quality by optimizing IVF techniques. In IVF procedures, oocytes and sperm are routinely co-incubated overnight, which may expose oocytes and zygotes to suboptimal culture conditions with increased reactive oxygen species (ROS) produced by sperm in this long term culture. As an attempt to avoid possible detrimental effects on the oocytes from long exposure to sperm, the brief co-incubation insemination protocol was developed. However, despite a number of studies in this area, it is unclear whether brief co-incubation improves the IVF outcomes compared with the standard overnight insemination protocol.

OBJECTIVES

This Cochrane review aimed to determine whether brief co-incubation of sperm and oocytes improves outcomes compared with the standard overnight insemination protocol for women undergoing IVF.

SEARCH METHODS

We searched the Cochrane Menstrual Disorders and Subfertility Group Register (14 June 2012), Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2012, 1st quarter), MEDLINE (1948 to 14 June 2012), EMBASE (1989 to 14 June 2012), PsycINFO (1806 to 14 June 2012) and CINAHL (1980 to 26 July 2012). In addition, we searched trials registers, reference lists of articles, conference proceedings (American Society for Reproductive Medicine (ASRM), European Society of Human Reproduction and Embryology (ESHRE)) and contacted experts in the field.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) comparing brief co-incubation of gametes with the standard overnight insemination protocol.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for inclusion and trial quality, and extracted data. Disagreements were resolved by discussion with a third author. Statistical analysis was performed using RevMan software.

MAIN RESULTS

Eight RCTs with 733 women in total that compared brief co-incubation and the standard insemination protocol were included. Live birth was not reported in the included studies. For ongoing pregnancy rate, there were 127 ongoing pregnancies in two trials including 426 women. The low quality evidence showed that brief co-incubation was associated with an increased ongoing pregnancy rate compared to the standard insemination protocol (pooled odds ratio (OR) 2.42, 95% confidence interval (CI) 1.55 to 3.77; P < 0.0001, I(2) = 0%). Measuring clinical pregnancy rate, there were 93 clinical pregnancies in three trials including 372 women. The low quality evidence showed that brief co-incubation was associated with a significantly higher clinical pregnancy rate than the overnight insemination protocol (pooled OR 2.36, 95% CI 1.45 to 3.85; P = 0.0006, I(2) = 0%). For the miscarriage rate, there were six miscarriages in one trial including 167 women. This low quality evidence suggested no significant difference in the odds of miscarriage between brief co-incubation and standard insemination (OR 1.98, 95% CI 0.35 to 11.09; P = 0.44).

AUTHORS' CONCLUSIONS

This review has provided evidence that brief co-incubation of sperm and oocytes may improve the ongoing pregnancy and clinical pregnancy rates for infertile women undergoing IVF cycles. More RCTs are required to assess whether brief co-incubation would contribute to a higher live birth rate and a lower miscarriage rate compared to the standard overnight insemination protocol.

Effects of cumulus cells removal after 6 h co-incubation of gametes on the outcomes of human IVF

PURPOSE

To investigate the effects of cumulus cells removal after 6 h co-incubation of gametes on the fertilization, polyspermy, multinucleation and clinical pregnancy rates in human IVF.

METHODS

A total of 1,200 IVF-ET cycles undergoing 6 h co-incubation of gametes in 2009 were included in this study. Inclusion criteria were: female age <38 years, first IVF treatment, with bi-ovary and normal ovarian response, e.g., 4 ~ 20 oocytes could be obtained. A 6 h period of co-incubation was applied in all IVF cycles. According to the history of infertility, cumulus cells were mechanically removed either 6 h post-insemination or 20 h post-insemination. For couples with primary infertility, or unexplained infertility, or mild oligospermia or asthenospermia, the cumulus cells were removed at 6 h of insemination for the polar body observation (6 h group, n = 565). Of these, 80 cycles received early rescue ICSI due to fertilization failure or low fertilization rate at 6 h of insemination. For couples with secondary infertility and normal semen analysis, the cumulus cells were removed at 20 h of insemination as routine (20 h group, n = 635). Of these, three cycles received late rescue ICSI due to fertilization failure at 20 h of insemination. Normal fertilization, polyspermy (≥3PN), multinucleation and clinical pregnancy rates were compared between the two groups (rescue ICSI cycles were not included in the comparison in both groups).

RESULTS

Significant difference (P < 0.05) was observed between the groups regarding polyspermy rates (7.48% in 6 h group and 9.22% in 20 h group). No difference was observed between the groups regarding normal fertilization rates (2PN rate) (64.89% in 6 h group and 65.74% in 20 h group). No difference was observed between the groups regarding multinucleation and clinical pregnancy rates (11.01% and 65.15% in 6 h group, 10.75% and 66.93% in 20 h group, respectively). The clinical pregnancy rate was 51.43% in cycles receiving early rescue ICSI, while no clinical pregnancy was obtained in cycles receiving late rescue ICSI.

CONCLUSION

The present results indicate that cumulus cells removal at 6 h of insemination is a relatively safe operation, which yielded comparable normal fertilization rate, multinucleation and clinical pregnancy rates compared with 20 h group. This protocol may be beneficial for early obsevation of fertilization failure and make early rescue ICSI possible.

Long-time exposure of mouse embryos to the sperm produces high levels of reactive oxygen species in culture medium and relates to poor embryo development

Small amounts of reactive oxygen species (ROS), metabolites of oxygen, are necessary for sperm-fertilizing capability. However, in excessive levels, their role in infertility has been extensively studied. The conventional in vitro fertilization (IVF) method employs a prolonged co-incubation of gametes for 16-18 h to reach fertilization. However, it has been shown that this long period might create high levels of ROS. We aimed at finding out whether ROS increases in vitro during prolonged incubation with fertilized oocytes and whether high level of ROS relates to poor embryo development. To confirm if levels of ROS relate to length of time, we measured the ROS levels in fertilization medium (FM), which contained mouse embryos exposed to spermatozoa. To evaluate the contribution of sperm in production of ROS, we measured the ROS in the medium with only sperm. The measurements were performed by chemiluminescence assay using luminol as a probe after 4 and 18 h of incubation separately. The ROS levels were significantly increased after 18 h as compared with 4 h (p < 0.0001). Moreover, ROS in the medium with only sperm was also increased after 18 h (p < 0.0001), demonstrating that they were generated either by spermatozoa or as a result of possible reaction of sperm with medium during prolonged incubation. In addition, we compared embryo development after 2, 4, 6, 8, 10, 12 and 18 h of incubation. The number of degenerated embryos exposed to sperm for 12 and 18 h was significantly higher than those exposed for 4 or 6 h (p < 0.01). These results demonstrate that ROS concentrations appear to be related to the length of incubation time, and their excessive levels have a negative effect on embryo development. We suggest reducing incubation time to at least 4 h.

Short gamete co-incubation during in vitro fertilization decreases the fertilization rate and does not improve embryo quality: a prospective auto controlled study

PURPOSE

Evaluate the effect of short gamete incubation on fertilization rate and embryo quality.

METHODS

A prospective study has been performed. Two thousand five hundred and forty seven sibling oocytes from 240 couples undergoing IVF attempts were allocated to a short (1 h) or a standard (18 h) insemination procedure. Diploid fertilization rate (two pronuclei, 2PN), polyspermy (>2PN) and embryo quality were compared.

RESULTS

The fertilization rate was statistically lower in the short insemination group compared to the standard insemination one (64.9% and 70.1%; P = 0.039), with a similar polyspermy rate observed between the two groups. A slight, but non significant, increase was observed concerning good embryo quality rate in the short insemination group when compared to the standard insemination, both at day 2 (60.1 vs. 58.1%; P = 0.06) and day 3 (53.2 vs. 48.5%; P = 0.22).

CONCLUSION

This new study highlights that a 1 h gamete exposure decreases the fertilization rate and does not improve embryo quality compared with a standard 18 h insemination procedure.

A prospective study, using sibling oocytes, examining the effect of 30 seconds versus 90 minutes gamete co-incubation in IVF

BACKGROUND

Traditionally oocytes have been exposed to sperm overnight, for 16-20 h. This long period of co-incubation, however, has been shown to create problems with high levels of reactive oxygen species (ROS), which may affect embryo viability and cause hardening of the zona pellucida. Recently, a positive effect of reducing the co-incubation time to 90-120 min was reported. The objective of this study was to evaluate whether a further reduction of the co-incubation period could benefit the outcome of IVF.

METHODS

In this prospective study, 777 sibling oocytes from 81 women undergoing IVF were divided via alternate allocation to co-incubation for either 30 s (ultrashort co-incubation) (group A) or for 90 min (standard co-incubation) (group B). Endpoints were normal fertilization (two-pronuclear, 2PN), polyspermy (>2PN), embryo quality (EQ), clinical pregnancy (CP) and implantation (IR).

RESULTS

The normal fertilization rates of the two groups were comparable: group A 58.6% versus group B 58.0%. Significantly lower rates of polyspermy were seen in group A compared to group B (2.8 versus 7.2%, P = 0.008). No statistically significant differences in EQ, CP or IR were seen.

CONCLUSION

This is the first study demonstrating the achievement of good fertilization rates in IVF with ultrashort co-incubation. Significantly lower rates of polyspermy were seen in the group with ultrashort compared to the standard co-incubation group. Further studies are, however, needed in order to evaluate whether ultrashort co-incubation has any effect on the outcome of IVF.