O-050 Vulnerability of human preimplantation embryos to SARS-CoV-2 infection

Presence of SARS-CoV-2, the virus responsible for COVID-19, has been reported in numerous organs and tissues of infected patients, including the reproductive system. The effects of COVID-19 on human reproduction remain poorly understood. While cases of intrauterine transmission between expectant mother and fetus have been documented, the impact of SARS-CoV-2 infection on early embryogenesis and establishment of a pregnancy are not known. This prompted us to ask if SARS-CoV-2 can infect embryos, since such an event could impact embryo viability and affect a subsequent pregnancy. We used a three-pronged approach to investigate this possibility: 1) Using RNA-seq and immunofluorescence, we learned that ACE2 and TMPRSS2, two factors required on target cells for SARS-CoV-2 entry, are co-expressed in cells of the trophectoderm in blastocyst-stage preimplantation embryos; 2) Using fluorescent reporter virions pseudotyped with Spike (S) glycoprotein from SARS-CoV-2, we observed robust infection of trophectoderm cells, and this permissiveness could be attenuated with blocking antibodies targeting S or ACE2; and 3) Exposing human blastocysts to live, fully infectious SARS-CoV-2, we detected cases of infection that compromised embryo health. Therefore, we identify a new human target tissue for SARS-CoV-2 with potential medical implications for reproductive health during the COVID-19 pandemic and its aftermath.

O-278 Prenatal outcomes of mosaic embryo transfer and neonatal assessment

Ever-improving PGT-A methodologies now make it feasible to routinely detect chromosomal mosaicism. What is the appropriate clinical management of those embryos? What is the impact on pregnancies and births when such embryos are transferred? Mosaicism is the consequence of chromosome-segregation errors at mitosis, resulting in a mix of cells with different chromosomal content. The transfer of embryos with evidence of diploid-aneuploid mosaicism in their PGT-A results has become relatively common practice, and numerous clinics have published their experiences with such transfers. On average, ‘mosaic’ embryos have decreased potential to establish a pregnancy and higher risk for miscarriage compared to ‘euploid’ embryos, but pregnancies reaching term seem to produce apparently healthy babies. These findings favor an expansion of the binary ‘normal vs abnormal’ classification system of PGT-A to include ‘mosaicism’ as a third category. Further data suggest that features of mosaicism detected with PGT-A associate with different clinical outcomes, namely the mosaic level (percent aneuploid cells) and the mosaic type (nature of aneuploidy). ‘Low level’ mosaicism is preferable to ‘high level’ mosaicism, and segmental abnormalities are preferable to aneuploidies affecting whole chromosomes. Therefore, the ‘mosaic’ category can be further refined for optimal ranking purposes in the clinic. While many mosaic embryo transfers have resulted in babies, systematic and detailed follow-up studies on pregnancies from such embryos are urgently needed. The present talk will give an update on the ongoing data collection effort by an international, multicenter consortium containing 1700+ ‘mosaic’ embryo transfers, neonate information from 500+ babies born from those transfers, and 380+ associated prenatal test results. Analysis of the data reveals that late-term pregnancies and babies from ‘mosaic’ and ‘euploid’ embryos have largely equivalent health, with a few notable exceptions.

O-201 Prenatal and postnatal outcome of mosaic embryo transfers: multicentric study of one thousand mosaic embryos diagnosed by preimplantation genetic testing with trophectoderm biopsy

Study question

To explore the effect of chromosomal mosaicism detected in preimplantation genetic testing (PGT-A) on prenatal and postnatal outcome of mosaic embryo pregnancies

Summary answer

No significant difference between euploid and mosaic embryos was observed in terms of weeks of gestation, average weight, and developmental defect of the babies born

What is known already

Mosaic embryos have the potential to implant and develop into healthy babies. Transfer of these embryos is now offered as an option for women who undergo IVF resulting in no euploid embryos. While, prenatal diagnosis has shown the depletion of chromosomal mosaicism in mosaic embryos, several concerns remain. For instance, the direct effects of different kind of mosaicism on prenatal/postnatal outcome and the possibility that intra-biopsy mosaicism in the TE is a poor predictor of the ploidy status of the ICM. Thus, there is certainly a need for comprehensive analyses of obstetrical and neonatal outcome data of transferred mosaic embryos.

Study design, size, duration

Compiled analysis from multicenter data on transfers of mosaic embryos (n = 1,000) and their outcome, with comparison to a euploid control group (n = 5,561). To explore the effect of embryonic mosaicism on newborns, we matched mosaic embryos resulting in a birth with a euploid embryo by a series of parameters (maternal age, embryo morphology, and indication for PGT-A). Prenatal tests and birth characteristics of > 200 neonates from mosaic embryo transfers were compared to > 200 euploid embryos.

Participants/materials, setting, methods

PGT-A was performed on blastocyst-stage embryos with 24-Chromosome whole genome amplification (WGA)-based Next Generation Sequencing (NGS). In accordance with established guidelines, embryos were categorized as mosaic when PGT-A results indicated 20-80% aneuploid content. Prenatal testing where performed in 30% of pregnancies with amniocentesis, 4% did an extra analysis for potential UPD for the suspected mosaic chromosome, and an additional 16% performed chorionic villus sampling (CVS) and 9.5% performed noninvasive prenatal testing (NIPT).

Main results and the role of chance

Of the 465 mosaic embryos that implanted, about 20% miscarried, and out of those, 75% were early spontaneous abortions. Of the pregnancies, 3 out of 368 were stillborn (2 out of them were twins that were extremely premature at 23 weeks, and the other died during pregnancy from a heart defect). The remaining 99% of those have been born or are late ongoing pregnancies at the time of analysis. Prenatal tests were performed in > 200 pregnancies and the vast majority tested normal. All 5 abnormal cases were amniocentesis tests showing microdeletions or insertions of sizes smaller than the resolution used during PGT-A, so they were unrelated to the mosaicism detected with PGT-A. In fact, in none of the cases did the prenatal test reflect the mosaicism detected at the embryonic stage. Matching each of the 162 mosaic embryos resulting in a birth with a euploid embryo, we found that the length of gestation was similar on average, and so was the average weight of the babies at birth. We also gathered information on the routine physical examination performed on babies at birth, and of those 162 babies from mosaic embryo transfers, none had obvious developmental defects or gross abnormalities.

Limitations, reasons for caution

Even though newborns resulting from mosaic embryo transfers in this study invariably appeared healthy by routine examination, concerns for long-term health cannot yet be entirely dispelled. The question must therefore be carefully considered by each clinic and patient situation.

Wider implications of the findings

Prenatal testing of > 200 pregnancies from mosaic embryo transfers showed no incidence of mosaicism that matched the PGT-A findings, indicating the involvement of self-corrective mechanisms. Pregnancy and obstetric data indicates that mosaic embryos prevailing through gestation and birth have similar chromosomal and physiological health compared to euploid embryos.

Trial registration number

none