Risk of monozygotic twinning with blastocyst transfer decreases over time: an 8-year experience

Maternal and perinatal risks for monozygotic twins conceived following frozen-thawed embryo transfer: a retrospective cohort study

BACKGROUND

The present study aimed to explore the maternal and perinatal risks in cases of monozygotic twins (MZT) following frozen-thawed embryo transfer (FET).

METHODS

All twin births that were conceived following FET from 2007 to 2021 at Shanghai Ninth People's Hospital in Shanghai, China were retrospectively reviewed. The exposure variable was twin type (monozygotic and dizygotic). The primary outcome was the incidence of neonatal death while secondary outcomes included hypertensive disorders of pregnancy, gestational diabetes, intrahepatic cholestasis of pregnancy, placenta previa, placental abruption, preterm premature rupture of the membranes, Cesarean delivery, gestational age, birth weight, weight discordance, stillbirth, birth defects, pneumonia, respiratory distress syndrome, necrotizing enterocolitis, and neonatal jaundice. Analysis of the outcomes was performed using logistic regression models to estimate odds ratios (ORs) and 95% confidence intervals (CIs). The causal mediation analysis was conducted. A doubly robust estimation model was used to validate the results. Kaplan-Meier method was used to calculate survival probability. The sensitivity analysis was performed with a propensity score-based patient-matching model.

RESULTS

Of 6101 dizygotic twin (DZT) and 164 MZT births conceived by FET, MZT showed an increased risk of neonatal death based on the multivariate logistic regression models (partially adjusted OR: 4.19; 95% CI, 1.23-10.8; fully adjusted OR: 4.95; 95% CI, 1.41-13.2). Similar results were obtained with the doubly robust estimation. Comparing MZT with DZT, the neonatal survival probability was lower for MZT (P < 0.05). The results were robust in the sensitivity analysis. Females with MZT pregnancies exhibited an elevated risk of preterm premature rupture of the membranes (adjusted OR: 2.42; 95% CI, 1.54-3.70). MZT were also associated with higher odds of preterm birth (prior to 37 weeks) (adjusted OR: 2.31; 95% CI, 1.48-3.67), low birth weight (adjusted OR: 1.92; 95% CI, 1.27-2.93), and small for gestational age (adjusted OR: 2.18; 95% CI, 1.21-3.69) in the fully adjusted analyses. The effect of MZT on neonatal death was partially mediated by preterm birth and low birth weight (P < 0.05).

CONCLUSIONS

This study indicates that MZT conceived by FET are related to an increased risk of neonatal death, emphasizing a potential need for comprehensive antenatal surveillance in these at-risk pregnancies.

Multiple Gestation after Elective Single-Embryo Transfer: A State-of-the-Art Review of Literature and Suggested Mechanisms

Background

Elective single-embryo transfers are being increasingly used to curb the increase in multiple gestation rates. However, it has been documented that single-embryo transfers could still result in twins and on rarer occasions in triplet pregnancies. Main Body. A literature review was done to highlight the possible mechanisms leading to embryonic splitting. In this review, the incidence of zygotic splitting was addressed and the notion of chorionicity was explained. Risk factors for zygotic splitting and suggested mechanisms for both twin and higher order pregnancies were suggested and discussed.

Conclusion

The hypotheses that we have so far remain unproven due to the rarity of zygotic splitting as well as the ethicolegal considerations of human embryo research. The presence of such incidents necessitates extensive counselling of the couple.

Pregnancy and neonatal outcomes of monozygotic twins resulting from assisted reproductive technology: a 10-year retrospective study

BACKGROUND

Monozygotic twins (MZTs) are associated with high risks of maternal and fetal complications. Even with the widely used elective single embryo transfer (SET), the risk of MZTs following assisted reproductive technology (ART) treatments remains. However, most studies of MZTs focused on the relevant etiology, with few studies describing pregnancy and neonatal outcomes.

METHODS

This retrospective cohort study included 19,081 SET cycles resulting from in-vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), preimplantation genetic testing (PGT) and testicular sperm aspiration (TESA) performed between January 2010 and July 2020 in a single university-based center. A total of 187 MZTs were included in this investigation. The main outcome measures were the incidence, pregnancy and neonatal outcomes of MZTs. Multivariate logistic regression analysis was performed to figure out the risk factors for pregnancy loss.

RESULTS

The overall rate of MZTs from ART treatment in SET cycles was 0.98%. No significant difference was found in the incidence of MZTs among the four groups (p = 0.259). The live birth rate of MZTs in the ICSI group (88.5%) was significantly more favorable than in the IVF, PGT and TESA groups (60.5%, 77.2% and 80%, respectively). IVF resulted in a significantly increased risk of pregnancy loss (39.4%) and early miscarriage (29.5%) in MZT pregnancies compared to ICSI (11.4%, 8.5%), PGT (22.7%, 16.6%) and TESA (20%, 13.3%). The total rate of twin-to-twin transfusion syndrome (TTTS) in MZTs was 2.7% (5/187); however, the TESA group had the highest rate at 20% and was significantly higher than the PGT group (p = 0.005). The four ART groups had no significant effect on the occurrence of congenital abnormalities or other neonatal outcomes in newborns from MZT pregnancies. Multivariate logistic regression analysis revealed that infertility duration, cause of infertility, the total dose of Gn used, history of miscarriages, and the number of miscarriages were not related to the risk of pregnancy loss (p > 0.05).

CONCLUSIONS

The rate of MZTs was similar among the four ART groups. The pregnancy loss and the early miscarriage rate of MZTs was increased in IVF patients. Neither the cause of infertility nor the history of miscarriage was correlated with the risk of pregnancy loss. MZTs in the TESA group had a higher risk of TTTS, placental effects influenced by sperm and paternally expressed genes may play a role. However, due to the small total number, studies with larger sample sizes are still needed to validate these result. Pregnancy and neonatal outcomes of MZTs after PGT treatment seem to be reassuring but the duration of the study was short, and long-term follow-up of the children is needed.

Assisted Reproduction and Discussion of Rare Cases in Monozygotic Twinning

Assisted reproductive technology is a crucial factor that increases the incidence of monozygotic twinning in humans. This article discusses the impact of various indicators in assisted reproductive technology studies on pregnancy outcomes, especially studies with a large number of clinical cases. Furthermore, three rare cases in multiples pregnancy are discussed: fetus papyraceous of a pair of male monozygotic twins in a set of triplets, two pairs of sesquizygotic twins with sex-discordance, and rare conjoined triplets.

Cleavage-stage versus blastocyst-stage embryo transfer in assisted reproductive technology

BACKGROUND

Advances in embryo culture media have led to a shift in in vitro fertilisation (IVF) practice from cleavage-stage embryo transfer to blastocyst-stage embryo transfer. The rationale for blastocyst-stage transfer is to improve both uterine and embryonic synchronicity and enable self selection of viable embryos, thus resulting in better live birth rates.

OBJECTIVES

To determine whether blastocyst-stage (day 5 to 6) embryo transfer improves the live birth rate (LBR) per fresh transfer, and other associated outcomes, compared with cleavage-stage (day 2 to 3) embryo transfer.

SEARCH METHODS

We searched the Cochrane Gynaecology and Fertility Group Specialised Register of controlled trials, CENTRAL, MEDLINE, Embase, PsycINFO, and CINAHL, from inception to October 2021. We also searched registers of ongoing trials and the reference lists of studies retrieved.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) which compared the effectiveness of IVF with blastocyst-stage embryo transfer versus IVF with cleavage-stage embryo transfer.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures recommended by Cochrane. Our primary outcomes were LBR per fresh transfer and cumulative clinical pregnancy rates (cCPR). Secondary outcomes were clinical pregnancy rate (CPR), multiple pregnancy, high-order multiple pregnancy, miscarriage (all following first embryo transfer), failure to transfer embryos, and whether supernumerary embryos were frozen for transfer at a later date (frozen-thawed embryo transfer). We assessed the overall quality of the evidence for the main comparisons using GRADE methods.

MAIN RESULTS

We included 32 RCTs (5821 couples or women). The live birth rate following fresh transfer was higher in the blastocyst-stage transfer group (odds ratio (OR) 1.27, 95% confidence interval (CI) 1.06 to 1.51; I² = 53%; 15 studies, 2219 women; low-quality evidence). This suggests that if 31% of women achieve live birth after fresh cleavage-stage transfer, between 32% and 41% would do so after fresh blastocyst-stage transfer. We are uncertain whether blastocyst-stage transfer improves the cCPR. A post hoc analysis showed that vitrification could increase the cCPR. This is an interesting finding that warrants further investigation when more studies using vitrification are published. The CPR was also higher in the blastocyst-stage transfer group, following fresh transfer (OR 1.25, 95% CI 1.12 to 1.39; I² = 51%; 32 studies, 5821 women; moderate-quality evidence). This suggests that if 39% of women achieve a clinical pregnancy after fresh cleavage-stage transfer, between 42% and 47% will probably do so after fresh blastocyst-stage transfer. We are uncertain whether blastocyst-stage transfer increases multiple pregnancy (OR 1.05, 95% CI 0.83 to 1.33; I² = 30%; 19 studies, 3019 women; low-quality evidence) or miscarriage rates (OR 1.12, 95% CI 0.90 to 1.38; I² = 24%; 22 studies, 4208 women; low-quality evidence). This suggests that if 9% of women have a multiple pregnancy after fresh cleavage-stage transfer, between 8% and 12% would do so after fresh blastocyst-stage transfer. However, a sensitivity analysis restricted only to studies with low or 'some concerns' for risk of bias, in the subgroup of equal number of embryos transferred, showed that blastocyst transfer probably increases the multiple pregnancy rate. Embryo freezing rates (when there are frozen supernumerary embryos for transfer at a later date) were lower in the blastocyst-stage transfer group (OR 0.48, 95% CI 0.40 to 0.57; I² = 84%; 14 studies, 2292 women; low-quality evidence). This suggests that if 60% of women have embryos frozen after cleavage-stage transfer, between 37% and 46% would do so after blastocyst-stage transfer. Failure to transfer any embryos was higher in the blastocyst transfer group (OR 2.50, 95% CI 1.76 to 3.55; I² = 36%; 17 studies, 2577 women; moderate-quality evidence). This suggests that if 1% of women have no embryos transferred in planned fresh cleavage-stage transfer, between 2% and 4% probably have no embryos transferred in planned fresh blastocyst-stage transfer. The evidence was of low quality for most outcomes. The main limitations were serious imprecision and serious risk of bias, associated with failure to describe acceptable methods of randomisation.

AUTHORS' CONCLUSIONS

There is low-quality evidence for live birth and moderate-quality evidence for clinical pregnancy that fresh blastocyst-stage transfer is associated with higher rates of both than fresh cleavage-stage transfer. We are uncertain whether blastocyst-stage transfer improves the cCPR derived from fresh and frozen-thawed cycles following a single oocyte retrieval. Although there is a benefit favouring blastocyst-stage transfer in fresh cycles, more evidence is needed to know whether the stage of transfer impacts on cumulative live birth and pregnancy rates. Future RCTs should report rates of live birth, cumulative live birth, and miscarriage. They should also evaluate women with a poor prognosis to enable those undergoing assisted reproductive technology (ART) and service providers to make well-informed decisions on the best treatment option available.

Multiple gestation associated with infertility therapy: a committee opinion

This Committee Opinion provides practitioners with suggestions to reduce the likelihood of iatrogenic multiple gestation resulting from infertility treatment. This document replaces the document of the same name previously published in 2012 (Fertil Steril 2012;97:825-34 by the American Society for Reproductive Medicine).

Blastocyst morphology is associated with the incidence of monozygotic twinning in assisted reproductive technology

BACKGROUND

An increased incidence of monozygotic twinning after a blastocyst transfer has been previously reported in assisted reproductive technology treatment. It is uncertain whether this phenomenon is due to the extended culture time, culture medium, or inherent blastocyst parameters.

OBJECTIVE

This study aimed to investigate the association between blastocyst parameters (in vitro culture time, blastocyst stage, and inner cell mass and trophectoderm grading) and the incidence of monozygotic twinning after assisted reproductive technology.

STUDY DESIGN

This was a retrospective cohort study employing data from a multicenter, large, electronic database from 4 academic hospitals. All clinical pregnancies after a single blastocyst transfer between January 2014 and February 2020 were included. Blastocyst morphology was evaluated based on the Gardner grading system, considering the blastocyst stage, and inner cell mass and trophectoderm grading (grades A, B, and C). Monozygotic twinning was defined as ≥2 fetal heartbeats in a single gestational sac or 2 gestational sacs with sex concordance at birth. The multivariable predicted marginal proportions from logistic regression models were used to compute adjusted relative risks for the association between blastocyst parameters and the incidence of monozygotic twinning.

RESULTS

The overall monozygotic twinning rate was 1.53% (402 of 26,254 cases). The monozygotic twinning was not associated with the culture time in vitro (day 5 vs day 6) or blastocyst stage (early, blastocyst, expanded, hatching, and hatched). Alternatively, monozygotic twinning was associated with lower inner cell mass grading (B vs A: adjusted relative risk, 1.67 [95 % confidence interval, 1.28-2.25]; C vs A: adjusted relative risk, 1.98 [95% confidence interval, 1.18-3.11]) and higher trophectoderm grading (B vs C: adjusted relative risk, 1.38 [95% confidence interval, 1.03-1.92]; A vs C: adjusted relative risk, 2.14 [95% confidence interval, 1.45-3.20]). The incidence of monozygotic twinning was the lowest in blastocysts with grade A inner cell mass and grade B or C trophectoderm (0.82%, as the reference) and the highest in blastocysts with grade B or C inner cell mass and grade A trophectoderm (2.40%; adjusted relative risk, 2.62; 95% confidence interval, 1.60-4.43). The incidence of monozygotic twinning in blastocysts with consistent inner cell mass or trophectoderm grading was somewhere in between (both A: 1.58%; adjusted relative risk, 1.86 [95% confidence interval, 1.23-3.04]; both B or C: 1.59%; adjusted relative risk, 1.84 [95% confidence interval, 1.29-2.90]).

CONCLUSION

Higher risk of monozygotic twinning was associated with blastocyst morphology specific to those blastocysts with loosely arranged inner cell mass cells combined with tightly packed trophectoderm cells.

Maternal age is associated with embryo splitting after single embryo transfer: a retrospective cohort study

PURPOSE

To determine whether maternal age has an impact on monozygotic twinning (MZT) rates in women undergoing single embryo transfer (SET).

METHODS

This is a retrospective cohort study analyzed for the incidence of MZT of all clinical pregnancies after a single embryo transfer was carried out between 2014 and 2018. The effect of different assisted reproductive technology (ART) parameters on the incidence of MZT was evaluated.

RESULTS

There were a total of 8459 cycles resulting in pregnancy during the study period. Of these pregnancies, 8236 were singletons and 223 were MZT. The preterm birth rate, miscarriage rate, and cesarean section rate were higher in MZT. Birth weight and gestational age at delivery were lower and smaller. In the univariate analysis, the risk of MZT was decreased with frozen embryo transfer (ET). A nonlinear relationship was observed between maternal age and MZT. A negative relationship between maternal age and MZT was observed in the patients' age ≥ 36 years.

CONCLUSION

Advanced maternal age was associated with a lower rate of MZT. A threshold female age of 36 years existed for lower MZT.

Double trouble? Impact of frozen embryo transfer on the monozygotic twinning rate: a retrospective cohort study from 8459 cycles

PURPOSE

To compare monozygotic twinning (MZT) rates in patients undergoing fresh embryo transfer (ET) and frozen embryo transfer.

METHODS

All clinical pregnancies after single ET carried out in our IVF center between 2014 and 2018 (n = 8459) were retrospectively analyzed for the incidence of MZT. MZT rate was compared in women who underwent fresh ET (n = 3876) and frozen ET (n = 4583).

RESULTS

There was a total of 120 MZT identified in the fresh ET group (3.10%) and 103 MZT in the frozen ET group (2.25%), which was significant (p = 0.015). In the univariate analysis, the risk of MZT was decreased with frozen embryo transfer (OR 0.72; 95% CI, 0.55-0.94, p = 0.016) and increased with mild stimulation protocol in the fresh cycle (OR 1.90; 95% CI, 1.04-3.45, p = 0.036). Multivariable logistic regression revealed that frozen embryo transfer was associated with a significant decrease risk of MZT (adjusted OR 0.66; 95% CI, 0.46-0.90, p = 0.011).

CONCLUSIONS

Frozen ET is associated with a lower risk of MZT.

Repeated triplets complicated by monochorionic diamniotic twins following assisted reproduction: a case report and literature review

BACKGROUND

Monochorionic twinning involves numerous maternal and fetal complications, triplets complicated by a monochorionic pair are at further increased risk. Here, we report a case of repeated triplets complicated by monochorionic diamniotic twins with successful pregnancy outcomes in a woman using autologous oocytes.

CASE PRESENTATION

A 30-year-old female undergoing embryo transfer with fresh and frozen embryo cycles with autologous oocytes. The two cycles were confirmed by transvaginal ultrasound to result in successful clinical pregnancies of triplets complicated by a monochorionic twinning. The first pregnancy resulted in a singleton delivery after a selective reduction of the monochorionic pair. The subsequent pregnancy resulted in a dichorionic diamniotic twin pregnancy after the heartbeat of one of the monochorionic twin fetuses stopped at 43 days after embryo transfer. Both of the pregnancies ended with successful live births.

CONCLUSIONS

Our case report of repeated triplets with monochorionic twins suggests the potential causes and risk factors of monochorionic twinning in assisted reproduction and raises concern regarding the timing of multifetal pregnancy reduction.

Risk factors for monozygotic twinning after in vitro fertilization: a systematic review and meta-analysis

OBJECTIVES

To establish the risk factors for monozygotic twin (MZT) and monochorionic twin (MCT) pregnancies after in vitro fertilization (IVF).

DESIGN

Systematic review and meta-analysis.

SETTING

Not applicable.

PATIENT(S)

Women who achieved MZT and non-MZT pregnancies through IVF.

INTERVENTION(S)

Systematic search of Medline from January 1995 to October 2018 with cross-checking of references from relevant articles in English.

MAIN OUTCOME MEASURE(S)

Possible risk factors for MZT or MCT pregnancies after IVF, comprising extended embryo culture, insemination method (conventional IVF and intracytoplasmic sperm injection [ICSI]), embryo biopsy for preimplantation genetic testing for aneuploidies or for monogenic/single-gene defects (PGT-A or PGT-M) programs, assisted hatching (AH), oocytes donation, female age, and embryo cryopreservation.

RESULT(S)

A total of 40 studies were included. Blastocyst transfer compared with cleavage-stage embryo transfer, and female age <35 years were associated with a statistically significant increase in the MZT and MCT pregnancy rate after IVF: (23 studies, OR 2.16, 95% CI, 1.74-2.68, I²=78%; 4 studies, OR 1.29; 95% CI, 1.03-1.62, I²=62%; and 3 studies, OR 1.90, 95% CI, 1.21-2.98, I²=59%; 2 studies, OR 2.34; 95% CI, 1.69-3.23, I²=0, respectively). Conventional IVF compared with ICSI and assisted hatching were associated with a statistically significantly increased risk of MZT pregnancy (9 studies, OR 1.19, 95% CI, 1.04-1.35, I²=0; 16 studies, OR 1.17, 95% CI, 1.09-1.27, I²=29%, respectively). Embryo biopsy for PGT-A or PGT-M, embryo cryopreservation, and oocytes donation were not associated with MZT pregnancies after IVF.

CONCLUSION(S)

Blastocyst transfer is associated with an increased risk of both MZT and MCT pregnancies after IVF. Further evidence is needed to clarify the impact of female age, insemination method and AH on the investigated outcomes.

Blastocyst culture and transfer in clinically assisted reproduction: a committee opinion

The purposes of this Practice Committee Opinion, which replaces the 2013 ASRM Practice Committee Opinion of the same name (Fertil Steril 2013; 99:667-72), are to review the literature regarding the clinical application of blastocyst transfer and identify the potential risks and laboratory issues related to the use of this technology. This document does not apply to patients undergoing blastocyst culture and transfer for preimplantation genetic testing.

Quadruple pregnancy after post-IVF/ICSI transfer of blastocysts

Clinical case of a quadruple pregnancy (monochorionic diamniotic and dichorionic diamniotic) after the transfer of two blastocysts generated by intracytoplasmic sperm injection (ICSI). This is the case of a 29-year-old woman patient with transfer of two blastocysts after long cultivation of 6 embryos generated by ICSI and vitrified on day +3. This revealed quadruple clinical pregnancy (monochorionic diamniotic and dichorionic diamniotic) of 56 days of evolution by transvaginal ultrasound. The couple decided to undergo a selective embryonic reduction of the monochorionic diamniotic pregnancy after receiving information about the risks arising from it. After that embryonic reduction the uncomplicated pregnancy continued until 36 weeks of gestation, achieving reproductive success with the birth of two babies alive and healthy.

The risk of secondary sex ratio imbalance and increased monozygotic twinning after blastocyst transfer: data from the Japan Environment and Children's Study

BACKGROUND

Some studies have suggested that blastocyst transfer is associated with i) imbalance in the secondary sex ratio (SSR) (which favors male offspring), ii) increased incidence of monozygotic twins (MZT). In contrast, others have not found these changes. In this study, we evaluated the association between blastocyst transfer and SSR and MZT, considering potential parental confounders.

METHODS

The Japan Environment and Children's Study is a large, nationwide longitudinal birth cohort study funded by the Ministry of the Environment of Japan. We used this large dataset, including 103,099 pregnancies, to further investigate the association between blastocyst transfer, SSR and MZT, using spontaneously conceived pregnancies, non-assisted reproductive technology (non-ART) treatment (intrauterine insemination and ovulation induction with timed intercourse) and cleavage stage embryo transfer for comparison. We evaluated the association with each group, the SSR, and the frequency of MZT, calculating the adjusted odds ratio (AOR) using multivariable logistic regression analyses, adjusting for potential parental confounders such as basic health and socioeconomic status.

RESULTS

For each group (spontaneous conception vs. non-ART treatment vs. cleavage stage embryo transfer vs. blastocyst transfer), the percentages of males were 51.3% vs 50.7% vs 48.9% vs 53.4% and the monozygotic twinning rates per pregnancy were 0.27% vs 0.11% vs 0.27% vs 0.99% respectively. Multivariate logistic regression analyses indicated that blastocyst transfer was significantly associated with a higher SSR and higher incidence of MZT than the other three groups (SSR: AOR 1.095, 95% CI1.001-1.198; MZT: AOR 4.229, 95% CI 2.614-6.684).

CONCLUSIONS

There are significant relationships between blastocyst transfer and SSR imbalance and a higher occurrence of MZT.

Determinants of monozygotic twinning in ART: a systematic review and a meta-analysis

BACKGROUND

The incidence of monozygotic twins (MZT) after ART appears to be higher than the incidence after spontaneous conceptions contradicting the aim of ART to avoid multiple pregnancies because of the associated risks.

OBJECTIVE AND RATIONALE

The aim was to study the frequency of MZT after IVF and ICSI and how it is influenced by the day of embryo transfer, maternal age, zona pellucida manipulation, controlled ovarian stimulation, stimulation protocol, culture media and embryo quality.

SEARCH METHODS

Original studies and reviews were identified by searching the PubMed, Embase and Cochrane databases up to March 2017. The inclusion criterion was publications focusing on the five study questions related to MZT in our study. The exclusion criteria were articles that did not include blastocyst transfer, were on non-humans, were not published in peer-reviewed journals, and were based only on case studies. All of the articles were categorized according to the Oxford Centre for Evidence-based Medicine's 'Levels of Evidence', and quality and risk of bias assessment was performed with 'The Cochrane Collaboration's Risk of Bias Tools'. A meta-analysis was performed to study the impact of the day of embryo transfer on the MZT rate.

OUTCOMES

The literature search resulted in a total of 42 articles, including 38 original studies, for analysis. The included original studies reported a MZT rate with blastocyst transfer from zero to 13.2%. Our meta-analysis found a higher frequency of MZT after blastocyst transfer compared with cleavage-stage embryos transfer: odds ratio = 2.18, 95% CI: 1.93-2.48 (fixed effect meta-analysis). A younger maternal age may increase the MZT rate, and recent studies regarding the use of zona pellucida manipulating techniques have disagreed with the previous suspicion of a higher MZT rate after the use of these methods. The extended culture to-blastocyst stage is a potential risk factor for MZT, but it is uncertain whether this phenomenon is due to the extended time, culture media or greater likelihood of younger oocytes to reach the blastocyst stage. An increased frequency of MZT following the GnRH-agonist suppression protocol has been suggested, as well as a decreased frequency of MZT with high gonadotrophin doses, which could reflect an age-related effect. Only limited literature has focused on the role of embryo morphology in the MZT rate, therefore, this issue remains unresolved.

WIDER IMPLICATIONS

We found blastocyst transfer to be a risk factor for MZT. Hence, the results of this meta-analysis may weaken the previously proposed view that greater experience with blastocyst transfer and improved culture media could decrease the high rate of MZT after blastocyst transfer. To minimize the rate of MZT and the associated complications, the mechanisms underlying blastocyst transfer and MZT pregnancy must be elucidated.

Identifying risk factors related to monozygotic twins after assisted reproductive technologies

OBJECTIVE

This secondary analysis aimed to identify the incidence and risk factors associated with monozygotic twins (MZTs) after assisted reproductive technology (ART).

STUDY DESIGN

In this retrospective cohort observational study, the treatment cycles were compared between MZT and non-MZT pregnancies using logistic regression analyses. Of the 11,501 patients with 13,225 pregnancies, 166 MZTs were diagnosed (1.44% in ART pregnant patients; 1.25% in pregnant cycles).

RESULTS

Results of the logistic analysis revealed that embryo stage at transfer and number of good-quality embryos were independent predictive factors for MZTs. The thresholds for two factors were 3.5 and 3.5. The efficacy of embryo stage at transfer and number of good-quality embryos for MZTs were evaluated using receiver-operating characteristic curves. The areas under the curve (AUCs) for these two parameters were 0.708 and 0.633, respectively. Adding number of good quality embryos increased the discriminative ability of the model (AUC = 0.745).

CONCLUSIONS

The incidence of MZTs, subsequent to ART, is quite high. Extended culture (≥3.5 days), together with the number of good-quality embryos (≥3.5), conferred the greatest risk of producing MZTs.

The effect of blastocyst transfer on newborn sex ratio and monozygotic twinning rate: an updated systematic review and meta-analysis

RESEARCH QUESTION

Is blastocyst transfer (BT) associated with a higher offspring secondary sex ratio and monozygotic twinning (MZT)?

DESIGN

A systematic search of PubMed/MEDLINE, Embase, Web of Science, Cochrane Library and Google Scholar databases was carried out for studies published between 1995 and May 2017 using relevant keywords and a meta-analysis performed on selected studies. The analysis was performed using Stata 12.0; odds ratios (OR) and 95% confidence intervals (CI) were used to assess the results for binary studies. Subgroup analyses and meta-regression were also conducted.

RESULTS

Twenty-six studies published between 2001 and May 2017 (sex ratio: 13, MZT: 12, and both sex ratio and MZT: 1) were identified. The analysis showed a significantly higher M/F ratio at birth (OR = 0.89, 95% CI: 0.86 to 0.93, I² = 19.8%) and a higher risk of MZT (OR = 0.37, 95% CI: 0.22 to 0.60, I² = 75.2%) after BT compared with cleavage-stage embryo transfer (CT). Furthermore, a subgroup analysis was performed based on studies published after 2009; results were found to be consistent with the 2009 meta-analysis.

CONCLUSIONS

This meta-analysis provides an update and stronger evidence to support the observation that BT is associated with a higher proportion of males and an increased risk of MZT. In clinical practice, these BT-associated neonatal outcomes should be taken into account when counselling infertility patients.

Bilateral tubal pregnancies after a single-embryo transfer

Case

To present an extremely rare case of bilateral tubal pregnancies following a single‐embryo transfer in a woman with a 4 year history of infertility prior to seeking assisted reproductive technology.

Outcome

A pregnancy resulted from the transfer of an embryo that had been thawed from a frozen blastocyst during a hormone replacement cycle. An ultrasound that was performed at 5 weeks and 5 days of gestation revealed a gestational sac, embryo, and heartbeat in the right fallopian tube and similar signs of a gestational sac in the left fallopian tube. A laparoscopy revealed clear signs of an ectopic pregnancy in the ampulla of the right fallopian tube. Signs of swelling also were seen in the ampulla of the left fallopian tube. As the possibility of bilateral tubal pregnancies could not be ruled out, both fallopian tubes were removed. Pathological tests revealed chorionic villi and trophoblasts in both the left and right fallopian tubes.

Conclusion

All previously reported cases of bilateral tubal pregnancies have been a result of multiple ovulations or multiple‐embryo transfer and no case of bilateral tubal pregnancies after a single‐embryo transfer has ever been reported. No genetic testing was performed; thus, it cannot be definitively stated that the divided chorionic villi and trophoblasts came from only one embryo.

Single Blastocyst Transfer: The Key to Reduce Multiple Pregnancy Rates Without Compromising the Live Birth Rate

BACKGROUND

Historically, to achieve higher pregnancy rates, multiple embryos were transferred after an in-vitro fertilisation (IVF). However, this practice is being reassessed, because it leads to multiple pregnancies that is known to cause adverse maternal and fetal outcomes.

AIM

To compare the pregnancy outcomes in fresh IVF or intracytoplasmic sperm injection (ICSI) cycles among women undergoing elective single blastocyst transfer (eSBT) vs. those undergoing double blastocyst transfer (DBT).

SETTINGS AND DESIGN

It is a retrospective data analysis of 582 patients undergoing fresh IVF/ICSI cycles performed from January 2012 to June 2015.

MATERIALS AND METHODS

Patients, who underwent IVF/ICSI and developed more than one blastocyst, were included in the study. Donor cycles were excluded from the study. All the embryos were cultured to blastocyst stage in sequential media followed by transfer of two blastocysts (DBT) or eSBT and cryopreservation of the remaining.

STATISTICAL ANALYSIS

Statistical analysis was performed using chi square test.

RESULTS

Out of 582 patients, in 149 patients one blastocyst was transferred and in 433 patients two blastocysts were transferred. There was no statistical difference in the biochemical pregnancy rate, clinical pregnancy rate and live birth rate in both the groups. Statistics demonstrated a significant drop in miscarriage rate in eSBT group. There was no incidence of twins in eSBT group, whereas twin birth rate per clinical pregnancy was 29.02% in DBT group.

CONCLUSION

Single blastocyst transfer is an effective method to reduce the risk of multiple births without compromising the pregnancy outcomes. Given the promising potential of vitrification; the remaining blastocyst can be cryopreserved.

Do ARTs affect the incidence of monozygotic twinning?

STUDY QUESTION

Does the manipulation of gametes or embryos during ARTs increase the risk for monozygotic twinning (MZT)?

SUMMARY ANSWER

Frozen embryo transfer (ET) is associated with a lower MZT rate, while blastocyst culture is associated with an increased risk of monozygotic pregnancy.

WHAT IS KNOWN ALREADY

Monozygotic twins have a higher risk for perinatal complications. Although an increased incidence of monozygotic pregnancies after ART has been previously reported, data regarding the possible impact of different laboratory procedures are conflicting.

STUDY DESIGN, SIZE, DURATION

All clinical pregnancies after single ET carried out in our centre between 2004 and 2013 (n = 6096) were retrospectively analysed for the incidence of MZT. The effect of different laboratory procedures on the incidence of MZT was evaluated.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The following ART risk factors were assessed: maternal age, type of ET (fresh versus frozen), zona pellucida (ZP) manipulation (specifically, ICSI, embryo biopsy and assisted hatching), use of donor oocytes, embryo stage at time of ET (cleavage, compaction, early or advanced blastocyst) and culture media.

MAIN RESULTS AND THE ROLE OF CHANCE

The overall MZT rate was 2.2% (136/6096). Frozen ET was associated with a significant reduction in MZT incidence (adjusted odds ratio (aOR) 0.48, 95% CI 0.29-0.80), while blastocyst transfer (early or advanced blastocyst) was associated with a significant increase in MZT risk (aOR 2.70, 95% CI 1.36-5.34; aOR 2.05, 95% CI 1.29-3.26, respectively). No significant differences were found between the MZT and singleton (non-MZT) groups regarding maternal age, the use of different ZP manipulation techniques, not type of culture media used.

LIMITATION, REASONS FOR CAUTION

This study is limited by its retrospective nature and the fact that monozygosity was not confirmed by genetic testing. Furthermore, since monozygotic pregnancy is a rare event, other ART parameters that may influence its incidence could not be assessed during our analysis.

WIDER IMPLICATION OF THE FINDINGS

Our findings warrant future studies designed to investigate the association between specific ART procedures and MZT, namely the potential risk of blastocyst transfer to increase MZT.

STUDY FUNDING/COMPETING INTERESTS

No external funding was used for this study. There are no conflicts of interest.

Cleavage stage versus blastocyst stage embryo transfer in assisted reproductive technology

BACKGROUND

Advances in cell culture media have led to a shift in in vitro fertilisation (IVF) practice from cleavage stage embryo transfer to blastocyst stage transfer. The rationale for blastocyst transfer is to improve both uterine and embryonic synchronicity and enable self selection of viable embryos, thus resulting in better live birth rates.

OBJECTIVES

To determine whether blastocyst stage (day 5 to 6) embryo transfers improve the live birth rate, and other associated outcomes, compared with cleavage stage (day 2 to 3) embryo transfers.

SEARCH METHODS

We searched the Cochrane Gynaecology and Fertility Group Specialised Register of controlled trials, Cochrane Central Register of Controlled Trials (CENTRAL; the Cochrane Library; 2016, Issue 4), MEDLINE, EMBASE, PsycINFO, CINAHL, and Bio extracts from inception to 4th April 2016. We also searched registers of ongoing trials and the reference lists of studies retrieved.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) which compared the effectiveness of blastocyst versus cleavage stage transfers.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures recommended by Cochrane. Our primary outcomes were live birth and cumulative clinical pregnancy rates. Secondary outcomes were clinical pregnancy, multiple pregnancy, high order pregnancy, miscarriage, failure to transfer embryos, and embryo freezing. We assessed the overall quality of the evidence for the main comparisons using GRADE methods.

MAIN RESULTS

We included 27 RCTs (4031 couples or women).The live birth rate following fresh transfer was higher in the blastocyst transfer group (odds ratio (OR) 1.48, 95% confidence interval (CI) 1.20 to 1.82; 13 RCTs, 1630 women, I(2) = 45%, low quality evidence) following fresh transfer. This suggests that if 29% of women achieve live birth after fresh cleavage stage transfer, between 32% and 42% would do so after fresh blastocyst stage transfer.There was no evidence of a difference between the groups in rates per couple of cumulative pregnancy following fresh and frozen-thawed transfer after one oocyte retrieval (OR 0.89, 95% CI 0.64 to 1.22; 5 RCTs, 632 women, I(2) = 71%, very low quality evidence).The clinical pregnancy rate was also higher in the blastocyst transfer group, following fresh transfer (OR 1.30, 95% CI 1.14 to 1.47; 27 RCTs, 4031 women, I(2) = 56%, moderate quality evidence). This suggests that if 36% of women achieve clinical pregnancy after fresh cleavage stage transfer, between 39% and 46% would do so after fresh blastocyst stage transfer.There was no evidence of a difference between the groups in rates of multiple pregnancy (OR 1.05, 95% CI 0.83 to 1.33; 19 RCTs, 3019 women, I(2) = 30%, low quality evidence), or miscarriage (OR 1.15, 95% CI 0.88 to 1.50; 18 RCTs, 2917 women, I(2) = 0%, low quality evidence). These data are incomplete as under 70% of studies reported these outcomes.Embryo freezing rates were lower in the blastocyst transfer group (OR 0.48, 95% CI 0.40 to 0.57; 14 RCTs, 2292 women, I(2) = 84%, low quality evidence). This suggests that if 60% of women have embryos frozen after cleavage stage transfer, between 37% and 46% would do so after blastocyst stage transfer. Failure to transfer any embryos was higher in the blastocyst transfer group (OR 2.50, 95% CI 1.76 to 3.55; 17 RCTs, 2577 women, I(2) = 36%, moderate quality evidence). This suggests that if 1% of women have no embryos transferred in (planned) fresh cleavage stage transfer, between 2% and 4% will have no embryos transferred in (planned) fresh blastocyst stage transfer.The evidence was of low quality for most outcomes. The main limitation was serious risk of bias, associated with failure to describe acceptable methods of randomisation, and unclear or high risk of attrition bias.

AUTHORS' CONCLUSIONS

There is low quality evidence for live birth and moderate quality evidence for clinical pregnancy that fresh blastocyst stage transfer is associated with higher rates than fresh cleavage stage transfer. There was no evidence of a difference between the groups in cumulative pregnancy rates derived from fresh and frozen-thawed cycles following a single oocyte retrieval, but the evidence for this outcome was very low quality. Thus, although there is a benefit favouring blastocyst transfer in fresh cycles, it remains unclear whether the day of transfer impacts on cumulative live birth and pregnancy rates. Future RCTs should report rates of live birth, cumulative live birth, and miscarriage to enable couples or women undergoing assisted reproductive technology (ART) and service providers to make well informed decisions on the best treatment option available.

Grade and looseness of the inner cell mass may lead to the development of monochorionic diamniotic twins

OBJECTIVE

To examine the relationship between the inner cell mass (ICM) grade and its morphological configuration on the occurrence of monochorionic diamniotic (M-D) twinning.

DESIGN

Retrospective embryo cohort study.

SETTING

Private IVF clinic.

PATIENT(S)

Evaluation of frozen-thawed single blastocyst transfers with hormone replacement treatment in 8,435. This cohort included 71 blastocysts and their ICMs observed by time-lapse photography.

INTERVENTION(S)

Any changes in configuration of the ICMs observed by time-lapse photography were analyzed retrospectively.

MAIN OUTCOME MEASURE(S)

The amount of loosening of blastomeres within the ICM was evaluated by time-lapse observations. The number of cells that were involved in the loosening process was also assessed. Both of these parameters were correlated with the type of monozygotic twinning that eventuated.

RESULT(S)

The M-D twinning incidence resulting from blastocysts with a high grade ICM (grade A) were transferred was 0.38% (3/796), whereas it was significantly higher, 1.38% (34/2,463), when blastocysts with a poorer (B and C) grade ICM were transferred. Among 71 transferred frozen-thawed blastocysts that were studied with time-lapse photography, there were two dichorionic diamniotic and one M-D twins. Careful observations of the embryo that resulted in the one M-D case, revealed that the ICM acquired a looser appearance due to decompaction of at least eight cells. This type of decompaction was not observed in the ICMs of other transferred blastocysts.

CONCLUSION(S)

The occurrence of M-D twinning may be avoided by excluding blastocysts that contain decompacting ICMs.

Estimating the Risk of Monochorionic Twins in IVF Pregnancies From the Perspective of a Prenatal Diagnosis Unit

The aim of the present work was to estimate the risk of monochorionic twin (MCT) pregnancies in in vitro fertilization (IVF) cycles using data from a prenatal diagnosis unit. This was a retrospective cross-sectional study reporting on the frequency of IVF pregnancies among women attending a prenatal diagnosis service specifically dedicated to the management of monochorionic pregnancies. The observed rate was compared with the local regional rate of IVF births (2.2%). A binomial distribution model was used to calculate the 95% CI of proportions. One hundred and forty-five monochorionic pregnancies were selected. Ten of these were achieved with IVF, corresponding to a rate of 6.9% (95% CI: 3.5–11.8), significantly higher than the background rate in the local population of 2.2%. When considering exclusively monochorionic pregnancies achieving delivery of two viable newborns (n = 132), the number of IVF pregnancies was nine (6.8%, 95% CI: 3.7–12.5). We did not detect major differences in pregnancy outcome between IVF and natural monochorionic pregnancies, with the exception of the proportion of newborns with a neonatal birth < 2,500 g (100% vs. 80%, p = .03). In conclusion, data obtained from the perspective of a prenatal diagnosis unit suggest that women undergoing IVF face a 3- to 4-fold increased risk of monochorionic pregnancies.

Monochorionic quadramniotic and triamniotic pregnancies following single embryo transfers: two case reports and a review of the literature

Purpose

The purpose of this study is to report two cases of monozygotic quadruplet and triplet pregnancies following single embryo transfer (ET).

Methods

A 29-year-old woman and a 34-year-old woman underwent ART treatment in two affiliated University based ART units. The first woman underwent ICSI with day 3 embryo biopsy for pre-implantation genetic diagnosis (PGD) followed by day 4 transfer, which resulted in a monochorionic quadramniotic (MCQA) quadruplet pregnancy. The second woman underwent conventional IVF with transfer of a single blastocyst, which resulted in a monochorionic triamniotic (MCTA) triplet pregnancy.

Results

The first patient underwent successful selective foetal reduction at 16 + 3 and 17 + 4 weeks of gestation. Two healthy twin girls were delivered by elective caesarean section at 35 + 6 weeks of gestation. The second patient underwent successful selective foetal reduction at 14 + 1 weeks of gestation. The remaining monochorionic diamniotic (MCDA) twins are well at the time of writing this article.

Conclusions

To our knowledge, these cases represent the first case of viable MCQA pregnancy following single ET in the world and the third case of a viable MCTA pregnancy following conventional IVF with single ET. Several factors including blastocyst stage transfer and zona pellucida manipulation have been thought to contribute to monozygotic twinning in the context of ART. These two cases add to the growing literature of monozygotic multiple pregnancies following ART.

The effect of single embryo transfer on perinatal outcomes in Japan

OBJECTIVE

In 2007 and 2008, the Japan Society for Reproductive Medicine and the Japan Society of Obstetrics and Gynecology issued a recommendation for single embryo transfer (SET). Thereafter, SET was implemented in 73% of in vitro fertilization (IVF) cases in Japan. The purpose of this study was to evaluate the effects of compliance with the SET recommendation on perinatal outcomes.

METHODS

An electronic audit of the perinatal database of the Japanese Society of Obstetrics and Gynecology was conducted from 2001 through 2010. The database comprised data of 610,726 women. Totally, 20,923 women conceived through IVF. To compare perinatal outcomes, these women were categorized into two study groups depending on whether they conceived before (2004-2005, n=3,865) or after (2009-2010, n=6,842) the SET recommendation statement was issued.

RESULTS

The proportion of women who conceived through IVF increased from 1.3% in 2001 to 4.8% in 2010. Compliance with the SET recommendation led to a decrease in the incidence of twin pregnancies (33.9% versus 13%, p<0.01), incidence of preterm delivery (odds ratio [OR]: 0.54, 95% confidence interval [CI]: 0.50-0.59), low birth weight (OR: 0.42, 95% CI: 0.39-0.45), and neonatal intensive care unit admission (OR 0.70, 95% CI 0.65-0.76), but an increase in the incidence of monochorionic twins (1.6% versus 2.5%, p<0.01).

CONCLUSION

Compliance with the SET recommendation improved perinatal outcomes by reducing the incidence of twin pregnancies.

The incidence of monozygotic twinning in assisted reproductive technology: analysis based on results from the 2010 Japanese ART national registry

PURPOSE

To assess the incidence of monozygotic twinning (MZT) among cases undergoing assisted reproductive technology (ART) treatment.

METHODS

We performed a retrospective observational study and analyzed the data of patients who were registered in the national ART registry system of Japan from January to December 2010; only the data of patients with single embryo transfer (ET) were included.

RESULTS

Of 30,405 pregnancies, 425 resulted in MZT following fresh and frozenthawed ET. The MZT incidence among women undergoing ART was 1.4 %. Multiple logistic regression analysis indicated that cases undergoing fresh and frozen-thawed ET, blastocyst transfer had a significantly increased MZT rate (P < 0.01). Assisted hatching (AH) and frozen-thawed ET and maternal age did not significantly affect the MZT incidence. Of 8510 fresh ET pregnancies, 104 resulted in MZT. Multiple logistic regression analysis indicated that blastocyst transfer significantly increased the MZT rate in cases undergoing fresh ET. Ovarian stimulation, intracytoplasmic sperm injection, AH, and maternal age did not significantly affect the MZT incidence.

CONCLUSIONS

Blastocyst transfer was associated with an increased MZT incidence. We have to be aware of the potential risk of MZT caused by blastocyst transfer. However, further studies are required to assess the correlation among specific AH types, embryo culture conditions, and MZT incidence.

Factors associated with monozygosity in assisted reproductive technology pregnancies and the risk of recurrence using linked cycles

OBJECTIVE

To evaluate factors associated with monozygosity (MZ) (number of fetal heartbeats on early ultrasound greater than the number of embryos transferred) and the risk of recurrence in subsequent pregnancies using a national assisted reproduction database.

DESIGN

Historical cohort study.

SETTING

Clinic-based data.

PATIENT(S)

197,327 pregnancies (including 2,824 with evidence of MZ) from cycles reported to the Society for Assisted Reproductive Technology Clinic Outcome Reporting System (SART CORS) between 2004 and 2010.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Evidence of MZ, adjusted odds ratios and their 95% confidence intervals computed from logistic regression models.

RESULT(S)

In the univariate analysis, the risk of MZ was increased with ovulation disorders, donor oocytes, gonadotropin-releasing hormone agonist (GnRH-a) suppression, assisted hatching (AZH), and day 5-6 transfer, and was decreased with higher follicle-stimulating hormone (FSH) doses (≥3,000 IU). In the multivariate analysis, the risk of MZ was increased with GnRH-a suppression, AZH, and decreased with intracytoplasmic sperm injection (ICSI) and higher FSH dose. The interaction showed that although MZ was more likely with day 5-6 embryos, AZH had a minimal nonsignificant effect, whereas in day 2-3 embryos, AZH had a substantial statistically significant effect. Only one woman had a recurrence of MZ in a subsequent assisted reproduction pregnancy, which is consistent with randomness.

CONCLUSION(S)

The risk of MZ was higher with fresh day 5-6 embryos, donor oocytes, GnRH-a suppression, lower FSH doses, and AZH (particularly with day 2-3 embryos).

WITHDRAWN: What makes them split? Identifying risk factors that lead to monozygotic twins after in vitro fertilization

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Theoretical model of the relationship between single embryo transfer rate and multiple pregnancy rate in Japan

The purpose of the present study was to examine the effect of single embryo transfer (SET) in assisted reproductive technology (ART) on the reduction of the multiple pregnancy rate. We also estimated the monozygotic (MZ) twinning rates according to the SET diffusion indirectly. A reverse sigmoid curve was assumed and examined using nationwide data of SET from 2007 to 2009 in Japan. The multiple pregnancy rate decreased almost linearly where the SET pregnancy rate was between about 40% and 80% of regression approximation. The linear approximation overestimated multiple pregnancy rates in an early period and underestimated multiple pregnancy rates in the final period. The multiple pregnancy rate seemed to be influenced by the improvement of the total pregnancy rate of ART in the early period and by the MZ twinning after SET in the final period. The estimated MZ twinning rate after SET was around 2%.

Cleavage stage versus blastocyst stage embryo transfer in assisted reproductive technology

BACKGROUND

Advances in cell culture media have led to a shift in in vitro fertilization (IVF) practice from early cleavage embryo transfer to blastocyst stage transfer. The rationale for blastocyst culture is to improve both uterine and embryonic synchronicity and enable self selection of viable embryos thus resulting in higher implantation rates.

OBJECTIVES

To determine if blastocyst stage (Day 5 to 6) embryo transfers (ETs) improve live birth rate and other associated outcomes compared with cleavage stage (Day 2 to 3) ETs.

SEARCH METHODS

Cochrane Menstrual Disorders and Subfertility Group Specialised Register of controlled trials, Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library), MEDLINE, EMBASE and Bio extracts. The last search date was 21 February 2012.

SELECTION CRITERIA

Trials were included if they were randomised and compared the effectiveness of early cleavage versus blastocyst stage transfers.

DATA COLLECTION AND ANALYSIS

Of the 50 trials that were identified, 23 randomised controlled trials (RCTs) met the inclusion criteria and were reviewed (five new studies were added in this update). The primary outcome was rate of live birth. Secondary outcomes were rates per couple of clinical pregnancy, cumulative clinical pregnancy, multiple pregnancy, high order pregnancy, miscarriage, failure to transfer embryos and cryopreservation. Quality assessment, data extraction and meta-analysis were performed following Cochrane guidelines.

MAIN RESULTS

Twelve RCTs reported live birth rates and there was evidence of a significant difference in live birth rate per couple favouring blastocyst culture (1510 women, Peto OR 1.40, 95% CI 1.13 to 1.74) (Day 2 to 3: 31%; Day 5 to 6: 38.8%, I(2) = 40%). This means that for a typical rate of 31% in clinics that use early cleavage stage cycles, the rate of live births would increase to 32% to 42% if clinics used blastocyst transfer.There was no difference in clinical pregnancy rate between early cleavage and blastocyst transfer in the 23 RCTs (Peto OR 1.14, 95% CI 0.99 to 1.32) (Day 2 to 3: 38.6%; Day 5 to 6: 41.6%) and no difference in miscarriage rate (13 RCTs, Peto OR 1.18, 95% CI 0.86 to 1.60). The four RCTs that reported cumulative pregnancy rates (266 women, Peto OR 1.58, 95% CI 1.11 to 2.25) (Day 2 to 3: 56.8%; Day 5 to 6: 46.3%) significantly favoured early cleavage. Embryo freezing rates (11 RCTs, 1729 women, Peto OR 2.88, 95% CI 2.35 to 3.51) and failure to transfer embryos (16 RCTs, 2459 women, OR 0.35, 95% CI 0.24 to 0.51) (Day 2 to 3: 3.4%; Day 5 to 6: 8.9%) favoured cleavage stage transfer.

AUTHORS' CONCLUSIONS

This review provides evidence that there is a small significant difference in live birth rates in favour of blastocyst transfer (Day 5 to 6) compared to cleavage stage transfer (Day 2 to 3). However, cumulative clinical pregnancy rates from cleavage stage (derived from fresh and thaw cycles) resulted in higher clinical pregnancy rates than from blastocyst cycles. The most likely explanation for this is the higher rates of frozen embryos and lower failure to transfer rates per couple obtained from cleavage stage protocols. Future RCTs should report miscarriage, live birth and cumulative live birth rates to enable ART consumers and service providers to make well informed decisions on the best treatment option available.

Culture systems: embryo culture and monozygotic twinning

The incidence of monozygotic twinning in pregnancies achieved with assisted reproductive technologies (ART) is significantly higher than spontaneously conceived pregnancies. The factors associated with ART that predispose the embryos to splitting are not well-characterized. Assisted hatching and extended embryo culture are two ART laboratory methods that have been risk factors for monozygotic twinning. The methods and strategies that may be employed to avoid monozygotic twinning are discussed in this chapter.

Age-Related Success with Elective Single versus Double Blastocyst Transfer

Background. Although the optimal outcome of assisted reproductive technology (ART) is a healthy singleton pregnancy, the rate of twin gestation from ART in women over the age of 35 is persistently high. Methods/Findings. We compared clinical pregnancy rates (PRs), ongoing pregnancy/live birth rates, and multiple gestation rates (MGRs) in 108 women who chose elective single blastocyst transfer (eSBT) to 415 women who chose elective double blastocyst transfer (eDBT) at a hospital-based IVF center. There was no significant difference in PR between eSBT and eDBT (57.4% versus 50.2%, P = 0.47) nor between eSBT and eDBT within each age group: <35, 35–37, 38–40, and >40. The risk of multiple gestations, however, was greatly increased between eSBT and eDBT (1.6 versus 32.4%, P < 0.00005), and this difference did not vary across age groups. Conclusion(s). Women undergoing eDBT are at uniformly high risk of multiple gestation regardless of age. eSBT appears to significantly lower the risk of multiple gestation without compromising PR.

Monozygotic twins with discordant karyotypes following preimplantation genetic screening and single embryo transfer: case report

PURPOSE

to report a case of monozygotic monochorial diamniotic twins with discordant karyotypes.

METHODS AND RESULTS

the pregnancy was achieved following a treatment cycle with intracytoplasmic sperm injection (ICSI) and preimplantation genetic screening (PGS) for chromosomes X, Y, 13, 16, 18, 21, 22. One embryo euploid for studied chromosomes was transferred. Prenatal ultrasonography revealed monozygotic twins. One fetus had growth retardation, multiple organ abnormalities and polyhydramnion. The other twin had normal ultrasound appearance. Delivery on week 29 of gestation resulted in the birth of two females, a stillborn twin with karyotype 45,XX,-13[12]/46,XX,r(13)[3] and a healthy twin with normal karyotype.

CONCLUSIONS

the discordance in the twins' karyotypes originated from a mosaic embryo. Structural chromosomal abnormality of the affected twin could not be revealed using standard PGS investigation. Embryo splitting occurred probably due to apoptotic process in an early stage of embryo development. Apoptosis represents one of the possible mechanisms which can explain the embryo twinning process globally.