Twinning in ART: Single embryo transfer policy

Cellular mechanisms of monozygotic twinning: clues from assisted reproduction

BACKGROUND

Monozygotic (MZ) twins are believed to arise from the fission of a single fertilized embryo at different stages. Monochorionic MZ twins, who share one chorion, originate from the splitting of the inner cell mass (ICM) within a single blastocyst. In the classic model for dichorionic MZ twins, the embryo splits before compaction, developing into two blastocysts. However, there are a growing number of ART cases where a single blastocyst transfer results in dichorionic MZ twins, indicating that embryo splitting may occur even after blastocyst formation.

OBJECTIVE AND RATIONALE

For monochorionic MZ twins, we conducted a comprehensive analysis of the cellular mechanisms involved in ICM splitting, drawing from both ART cases and animal experiments. In addition, we critically re-examine the classic early splitting model for dichorionic MZ twins. We explore cellular mechanisms leading to two separated blastocysts in ART, potentially causing dichorionic MZ twins.

SEARCH METHODS

Relevant studies including research articles, reviews, and conference papers were searched in the PubMed database. Cases of MZ twins from IVF clinics were found by using combinations of terms including 'monozygotic twins' with 'IVF case report', 'ART', 'single embryo transfer', or 'dichorionic'. The papers retrieved were categorized based on the implicated mechanisms or as those with unexplained mechanisms. Animal experiments relating to MZ twins were found using 'mouse embryo monozygotic twins', 'mouse 8-shaped hatching', 'zebrafish janus mutant', and 'nine-banded armadillo embryo', along with literature collected through day-to-day reading. The search was limited to articles in English, with no restrictions on publication date or species.

OUTCOMES

For monochorionic MZ twins, ART cases and mouse experiments demonstrate evidence that a looser ICM in blastocysts has an increased chance of ICM separation. Physical forces facilitated by blastocoel formation or 8-shaped hatching are exerted on the ICM, resulting in monochorionic MZ twins. For dichorionic MZ twins, the classic model resembles artificial cloning of mouse embryos in vitro, requiring strictly controlled splitting forces, re-joining prevention, and proper aggregation, which allows the formation of two separate human blastocysts under physiological circumstances. In contrast, ART procedures involving the transfer of a single blastocysts after atypical hatching or vitrified-warmed cycles might lead to blastocyst separation. Differences in morphology, molecular mechanisms, and timing across various animal model systems for MZ twinning can impede this research field. As discussed in future directions, recent developments of innovative in vitro models of human embryos may offer promising avenues for providing fundamental novel insights into the cellular mechanisms of MZ twinning during human embryogenesis.

WIDER IMPLICATIONS

Twin pregnancies pose high risks to both the fetuses and the mother. While single embryo transfer is commonly employed to prevent dizygotic twin pregnancies in ART, it cannot prevent the occurrence of MZ twins. Drawing from our understanding of the cellular mechanisms underlying monochorionic and dichorionic MZ twinning, along with insights into the genetic mechanisms, could enable improved prediction, prevention, and even intervention strategies during ART procedures.

REGISTRAITON NUMBER

N/A.

Gestational carrier cycles: embryology trends, national guideline compliance, and resultant perinatal outcomes in the United States, 2014-2020

BACKGROUND

The increased use of gestational carriers has expanded family-building opportunities for people and couples unable to carry pregnancies on their own. National American Society of Reproductive Medicine guidelines for gestational carriers have changed over time to reflect advances in reproductive technology and mounting evidence supporting the medical benefits associated with singleton gestations.

OBJECTIVE

Assess changes in gestational carrier cycle practice patterns and resultant pregnancy outcomes in the United States in relation to changing national American Society of Reproductive Medicine guidelines, which changed in 2013 and 2017.

STUDY DESIGN

This retrospective study used data from the Society for Assisted Reproductive Technology Clinic Outcomes Reporting System and included all cycles that were reported from 2014-2020 involving an embryo transfer to a gestational carrier. Binomial regression models evaluated trends in preimplantation genetic testing for aneuploidy, American Society of Reproductive Medicine guideline adherence, number of embryos transferred, and pregnancy outcomes over time.

RESULTS

Of the 40,177 gestational carrier transfer cycles from 2014-2020, there was a significant increase in frozen-thawed cycles (41.3% increase), use of assisted hatching (53.4% increase), intracytoplasmic sperm injection (50.0% increase), and preimplantation genetic testing for aneuploidy (155.7% increase). The likelihood of preimplantation genetic testing for aneuploidy was higher in 2020 than in 2014 for autologous oocyte transfers to gestational carriers, both for those aged ≥38 years (adjusted relative risk, 2.38 [95% confidence interval, 2.11-2.70]) and than those aged <38 years (adjusted relative risk, 2.85 [95% confidence interval, 2.58-3.15]). As preimplantation genetic testing for aneuploidy usage increased, single embryo transfer rose for both autologous (adjusted relative risk, 2.22 [95% confidence interval, 1.94-2.50]) and donor cycles (relative risk, 1.91 [95% confidence interval, 1.81-2.02]). This shift toward single embryo transfer corresponded with a decrease in multiple embryo transfer by 79.2% and subsequent decreases in multiple gestations by 68.8% in donor and 73.6% in autologous oocyte cycles from 2014-2020. Gestational carrier cycles remained highly adherent to changing American Society of Reproductive Medicine guidelines throughout the study period. Among live births, there was a 19.4% and 7.9% increase in term deliveries among donor and autologous oocyte cycles, respectively, from 2014 to 2020.

CONCLUSION

Practice patterns have drastically changed throughout the study period, with major increases in the use of preimplantation genetic testing for aneuploidy, intracytoplasmic sperm injection, assisted hatching, and frozen transfers. In response to changing American Society of Reproductive Medicine guidelines, the use of multiple embryo transfers has decreased for gestational carrier cycles with subsequent decreases in multiple gestations and miscarriages and slight increases in live birth rates.

Risk assessment of patients with underlying health conditions who present for IVF treatment

The increasing number of women with underlying health conditions seeking in vitro fertilization (IVF) necessitates a comprehensive risk assessment framework tailored to their needs. This review aims to provide a practical framework for IVF specialists to systematically assess and manage the risks associated with medically complex patients. The GRASP mnemonic (Genetics, Retrieval, Anaesthetics, Stimulation, Pregnancy) is introduced to facilitate a thorough risk assessment process. The review emphasizes the importance of obtaining detailed medical histories, corroborating information from other healthcare providers, and involving maternal medicine specialists in pre-pregnancy counselling. Furthermore, it highlights the ethical considerations of informed consent, advocating for fertility specialists to take a central role in coordinating care and ensuring patient understanding of risks. Continuous health evaluation throughout the IVF process and clear communication of risks are crucial for improving patient outcomes.

Multifetal pregnancy reductions and selective fetocide in a tertiary referral center - a retrospective cohort study

OBJECTIVES

Multiple pregnancies involve several complications, most often prematurity, but also higher anomaly rates. Reducing fetuses generally improves pregnancy outcomes. We conducted this study to evaluate the obstetrical and neonatal results after multifetal pregnancy reduction (MFPR) in the largest tertiary hospital in Finland.

METHODS

This retrospective cohort study included all MFPR managed in Helsinki University Hospital during a 13 year period (2007-2019). Data on pregnancies, parturients and newborns were collected from patient files. The number of fetuses, chorionicities and amnionicities were defined in first-trimester ultrasound screening.

RESULTS

There were 54 MFPR cases included in the final analyses. Most often the reduction was from twins to singletons (n=34, 63 %). Majority of these (25/34, 73.5 %) were due to co-twin anomaly. Triplets (n=16, 29.6 %) were reduced to twins (n=7, 13 %) or singletons (n=9, 16.7 %), quadruplets (n=2, 3.7 %) and quintuplets (n=2, 3.7 %) to twins. Most (33/54, 61.1 %) MFPR procedures were done by 15+0 weeks of gestation. There were six miscarriages after MFPR and one early co-twin miscarriage. In the remaining 47 pregnancies that continued as twins (n=7, 14.9 %) or singletons (n=40, 85.1 %) the liveborn rate was 90 % for one fetus and 71.4 % for two fetuses.

CONCLUSIONS

Most MFPR cases were pregnancies with an anomalous co-twin. The whole pregnancy loss risk was 11.1 % after MFPR. The majority (70.6 %) of twins were spontaneous, whereas all quadruplets, quintuplets, and 56.3 % of triplets were assisted reproductive technologies (ART) pregnancies. Careful counselling should be an essential part of obstetrical care in multiple pregnancies, which should be referred to fetomaternal units for MFPR option.

Blastocyst telomere length predicts successful implantation after frozen-thawed embryo transfer

STUDY QUESTION

Do embryos with longer telomere length (TL) at the blastocyst stage have a higher capacity to survive after frozen-thawed embryo transfer (FET)?

SUMMARY ANSWER

Digitally estimated TL using low-pass whole genome sequencing (WGS) data from the preimplantation genetic testing for aneuploidy (PGT-A) process demonstrates that blastocyst TL is the most essential factor associated with likelihood of implantation.

WHAT IS KNOWN ALREADY

The lifetime TL is established in the early cleavage cycles following fertilization through a recombination-based lengthening mechanism and starts erosion beyond the blastocyst stage. In addition, a telomerase-mediated slow erosion of TL in human fetuses has been observed from a gestational age of 6-11 weeks. Finally, an abnormal shortening of telomeres is likely involved in embryo loss during early development.

STUDY DESIGN SIZE DURATION

Blastocyst samples were obtained from patients who underwent PGT-A and FET in an IVF center from March 2015 to May 2018. Digitally estimated mitochondrial copy number (mtCN) and TL were used to study associations with the implantation potential of each embryo.

PARTICIPANTS/MATERIALS SETTING AND METHODS

In total, 965 blastocysts from 232 cycles (164 patients) were available to investigate the biological and clinical relevance of TL. A WGS-based workflow was applied to determine the ploidy of each embryo. Data from low-pass WGS-PGT-A were used to estimate the mtCN and TL for each embryo. Single-variant and multi-variant logistic regression, decision tree, and random forest models were applied to study various factors in association with the implantation potential of each embryo.

MAIN RESULTS AND THE ROLE OF CHANCE

Of the 965 blastocysts originally available, only 216 underwent FET. While mtCN from the transferred embryos is significantly associated with the ploidy call of each embryo, mtCN has no role in impacting IVF outcomes after an embryo transfer in these women. The results indicate that mtCN is a marker of embryo aneuploidy. On the other hand, digitally estimated TL is the most prominent univariant factor and showed a significant positive association with pregnancy outcomes (P < 0.01, odds ratio 79.1). We combined several maternal and embryo parameters to study the joint effects on successful implantation. The machine learning models, namely decision tree and random forest, were trained and yielded classification accuracy of 0.82 and 0.91, respectively. Taken together, these results support the vital role of TL in governing implantation potential, perhaps through the ability to control embryo survival after transfer.

LIMITATIONS REASONS FOR CAUTION

The small sample size limits our study as only 216 blastocysts were transferred. The number was further reduced to 153 blastocysts, where pregnancy outcomes could be accurately traced. The other limitation of this study is that all data were collected from a single IVF center. The uniform and controlled operation of IVF cycles in a single center may cause selection bias.

WIDER IMPLICATIONS OF THE FINDINGS

We present novel findings to show that digitally estimated TL at the blastocyst stage is a predictor of pregnancy capacity after a FET cycle. As elective single-embryo transfer has become the mainstream direction in reproductive medicine, prioritizing embryos based on their implantation potential is crucial for clinical infertility treatment in order to reduce twin pregnancy rate and the time to pregnancy in an IVF center. The AI-powered, random forest prediction model established in this study thus provides a way to improve clinical practice and optimize the chances for people with fertility problems to achieve parenthood.

STUDY FUNDING/COMPETING INTERESTS

This study was supported by a grant from the National Science and Technology Council, Taiwan (MOST 108-2321-B-006-013 -). There were no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Higher risk of preterm twin delivery among shorter nulliparous women

OBJECTIVE

To determine if maternal height in nulliparous women influences pregnancy results in twin pregnancies.

MATERIAL AND METHODS

Retrospective cohort analysis evaluating twin pregnancies followed at Centro Hospitalar Universitário Lisboa Central, between 1995 and 2020. Of the 2900 pregnancies followed in that period, 886 nulliparous women with dichorionic twin pregnancies were selected. Two groups were considered: A - maternal height <163 cm (

RESULT(S)

PTB rates decreased along increasing maternal height. The comparison between group A and group B revealed no statistically significant differences in maternal characteristics (age, mode of conception - spontaneous or ART pregnancies, or BMI). Statistically significant differences were found in mean gestational age at birth (35.1 ± 1.8 vs. 36.0 ± 2.6 wks), PTB rates < 32, 34 and 36 wks, OR: 3.2, 2.3 and 2.4 respectively, p < 0.01. Shorter women had a 1.7× and 2.6× increased risk for significantly low (<2500 g) and very low (<1500 g) newborn birth weight (BW), respectively, and a 40 % increased risk of Cesarian delivery. No significant differences were shown with respect to stillbirths, neonatal and perinatal deaths, which had a low incidence in this study. In ART pregnancies we found the same results regarding PTB rates and newborn birthweight in shorter women. In Logistic Regression analysis, maternal height

CONCLUSION

Increased pregnancy risk in nulliparous shorter women should be taken into consideration in double embryo transfers.

Collapse

Key Words

• Art
• Dichorionic twins
• Maternal height
• Nulliparous women
• Perinatal outcomes

Collapse

MESH Headings

• Pregnancy
• Infant, Newborn
• Female
• Humans
• Infant
• Pregnancy, Twin
• Stillbirth
• Retrospective Studies
• Cesarean Section/adverse effects
• Premature Birth/epidemiology
• Infant, Very Low Birth Weight
• Birth Weight

Collapse

Grants Collapse

Affiliation(s)

Teresinha Simões Department of Maternal-Fetal Medicine, Maternity Dr. Alfredo da Costa, Centro Hospitalar Lisboa Central and Nova Medical School, Lisbon, Portugal; Department of Reproductive Medicine, Maternity Dr. Alfredo da Costa, Centro Hospitalar Lisboa Central and Nova Medical School, Lisbon, Portugal.
Inês Pereira Department of Maternal-Fetal Medicine, Maternity Dr. Alfredo da Costa, Centro Hospitalar Lisboa Central, Lisbon, Portugal
Laura Gomes Department of Maternal-Fetal Medicine, Maternity Dr. Alfredo da Costa, Centro Hospitalar Lisboa Central, Lisbon, Portugal
Sofia Brás Department of Maternal-Fetal Medicine, Maternity Dr. Alfredo da Costa, Centro Hospitalar Lisboa Central, Lisbon, Portugal
Isabel Nogueira Department of Maternal-Fetal Medicine, Maternity Dr. Alfredo da Costa, Centro Hospitalar Lisboa Central, Lisbon, Portugal
Alexandra Queirós Department of Maternal-Fetal Medicine, Prenatal Diagnosis Unit Maternity Dr. Alfredo da Costa, Centro Hospitalar Lisboa Central and Nova Medical School, Lisbon, Portugal

Collapse

Culture conditions in the IVF laboratory: state of the ART and possible new directions

In the last four decades, the assisted reproductive technology (ART) field has witnessed advances, resulting in improving pregnancy rates and diminishing complications, in particular reduced incidence of multiple births. These improvements are secondary to advanced knowledge on embryonic physiology and metabolism, resulting in the ability to design new and improved culture conditions. Indeed, the incubator represents only a surrogate of the oviduct and uterus, and the culture conditions are only imitating the physiological environment of the female reproductive tract. In vivo, the embryo travels through a dynamic and changing environment from the oviduct to the uterus, while in vitro, the embryo is cultured in a static fashion. Importantly, while culture media play a critical role in optimising embryo development, a large host of additional factors are equally important. Additional potential variables, including but not limited to pH, temperature, osmolality, gas concentrations and light exposure need to be carefully controlled to prevent stress and permit optimal implantation potential. This manuscript will provide an overview of how different current culture conditions may affect oocyte and embryo viability with particular focus on human literature.

Which sperm parameter limits could really guide the clinical decision in assisted reproduction?

BACKGROUND

The predictive role of sperm motility and morphology was recently detected in a large sample of more than 20000 assisted reproductive technology (ART) fresh cycles. However, the complete ART procedure consisted of both fresh and frozen-embryos transfers and only a comprehensive evaluation of the entire process could really confirm if these parameters really predict the ART success. The aim of the study was to evaluate which sperm parameter could predict the success of ART.

METHODS

A retrospective, real-world data analysis was performed, enrolling all couples attending ART from 2008 to 2021, including both fresh and frozen cycles and both in vitro fertilization (IVF) and intra-cytoplasmic sperm injection (ICSI) procedures.

RESULTS

Fresh cycles success (considering live birth rate) was predicted by female age (1.04 [1.02-1.06]), injected oocytes (0.96 [0.93-0.99]), embryo number (0.79 [0.75-0.83]) and progressive sperm motility (0.98 [0.97-0.99]). On the contrary, frozen cycle outcomes were predicted only by sperm motility (0.97 [0.95-0.99]). This prediction was confirmed in IVF but not in ICSI cycles.

CONCLUSION

Both female and male parameters predicted the ART success considering the entire path. However, frozen cycle success was predicted only by progressive sperm motility in IVF cycles, suggesting that the potential amelioration of this male parameter is relevant to improve ART success. Those couples expected to obtain the highest embryos after fertilization (low female age and better semen parameters) will have more attempts with frozen cycles and thus would benefit from a potential treatment focused to improve sperm parameters.

Human Blastocyst Components Detection Using Multiscale Aggregation Semantic Segmentation Network for Embryonic Analysis

Infertility is one of the most important health concerns worldwide. It is characterized by not being successful of pregnancy after some periods of periodic unprotected sexual intercourse. In vitro fertilization (IVF) is an assisted reproduction technique that efficiently addresses infertility. IVF replaces the actual mode of reproduction through a manual procedure wherein embryos are cultivated in a controlled laboratory environment until they reach the blastocyst stage. The standard IVF procedure includes the transfer of one or two blastocysts from several blastocysts that are grown in a controlled environment. The morphometric properties of blastocysts with their compartments such as trophectoderm (TE), zona pellucida (ZP), inner cell mass (ICM), and blastocoel (BL), are analyzed through manual microscopic analysis to predict viability. Deep learning has been extensively used for medical diagnosis and analysis and can be a powerful tool to automate the morphological analysis of human blastocysts. However, the existing approaches are inaccurate and require extensive preprocessing and expensive architectures. Thus, to cope with the automatic detection of blastocyst components, this study proposed a novel multiscale aggregation semantic segmentation network (MASS-Net) that combined four different scales via depth-wise concatenation. The extensive use of depthwise separable convolutions resulted in a decrease in the number of trainable parameters. Further, the innovative multiscale design provided rich spatial information of different resolutions, thereby achieving good segmentation performance without a very deep architecture. MASS-Net utilized 2.06 million trainable parameters and accurately detects TE, ZP, ICM, and BL without using preprocessing stages. Moreover, it can provide a separate binary mask for each blastocyst component simultaneously, and these masks provide the structure of each component for embryonic analysis. Further, the proposed MASS-Net was evaluated using publicly available human blastocyst (microscopic) imaging data. The experimental results revealed that it can effectively detect TE, ZP, ICM, and BL with mean Jaccard indices of 79.08, 84.69, 85.88%, and 89.28%, respectively, for embryological analysis, which was higher than those of the state-of-the-art methods.