BIRTH OF TWENTY-SEVEN HEALTHY BABIES FOLLOWING TRANSFER OF FRESH AND FROZEN- THAWED EMBRYOS DERIVED FROM MONOPRONUCLEAR ZYGOTES: A RETROSPECTIVE STUDY

If fertilized zygotes normally display 2 pronuclei (PN) 16 to 18 hours post insemination, abnormal fertilization patterns (0, 1 or >2 PN) are daily observed in IVF labs. Multiple PN zygotes (>2) are generally discarded due to an increased risk of aneuploidy, but the decision to transfer or not 1PN-derived embryos remains controversial.
The aims of our study were to analyze the neonatal outcomes of fresh/frozen-thawed embryos derived from 1PN zygotes, and to evaluate the influence of the fertilization method.
To answer these questions, data were retrospectively collected from cycles performed between January 2018 and December 2022. At first, fresh cycles were analyzed for the comparative fate of 1PN zygotes (n=1234) following conventional in vitro fertilization (IVF; n=648) or intracytoplasmic sperm injection (ICSI; n=586), as well as the results of the 64 transfers of 1PN-derived embryos (pregnancy rate (PR) and outcome of pregnancies). This pregnancy follow-up was also applied to 167 transfers of frozen-thawed 1PN-derived embryos.
In fresh cycles, 46% of the 1PN zygotes gave rise to embryos of sufficient quality to be transferred or frozen (day 3 or 5/6). This rate decreased to 33% in the fresh ICSI cycles. Blastulation rate was also more important (but not significantly) in IVF group (44%) in comparison to ICSI group (20%).
The fresh embryo transfers (32 in each fertilization group) allowed 7 pregnancies in the IVF group (PR=21.9%) as compared to 4 pregnancies in the ICSI group (PR=12.5%). The 7 IVF pregnancies ended in 4 deliveries of healthy newborns, 2 miscarriages and one pregnancy still ongoing. In the ICSI group, 1 birth of a healthy newborn and 3 miscarriages were observed.
In frozen/thawed cycles, thirty-six pregnancies were obtained out of the 167 transfers. A non-significative difference was observed between embryos derived from IVF cycles (PR=26%) and ICSI cycles (PR=16%) with respectively 15 and 6 healthy babies born. Two pregnancies in each group are still ongoing.
In conclusion, we observed better outcomes for 1PN zygotes in IVF cycles in comparison to ICSI cycles. Our center policy to transfer good quality 1PN-derived embryos (231 transfers in this study) allowed the birth of 27 healthy babies.