Authors: Davis, A.1, Bopp, B.2, Will, M.2, Anspach Will, E.2, O’Leary, K.2, Adaniya, G.1

Objective: Embryos fully enclosed in the zona pellucida (ZP) may survive freeze and warm processes better than fully hatched embryos.  The objective of this study is to discover if the position of the inner cell mass (ICM) inside or outside the ZP affects the embryo potential on pregnancy rates after freezing and warming when the embryo is not fully hatched.  This comparison will find if the ICM outside of the ZP leads to a difference in embryo potential.

Design: Retrospective study in a private assisted reproductive technology program.

Materials and Methods: The study examines a total of 1,190 single frozen embryo transfers of PGT-A tested euploid embryos created with autologous oocytes from January 2019 to December 2021.  At the time of transfer, it was noted if the embryo was fully enclosed in the ZP, if the inner cell mass was inside or outside the ZP, or if the embryo was fully hatched out of the ZP.  The embryos were classified into 3 groups: (A) not fully hatched, ICM inside the ZP (N=847), (B) not fully hatched, ICM outside the ZP (N=230), and (C) fully hatched (N=113).  The positive HCG (+HCG) rates and clinical pregnancy (CIG) rates were compared between the three groups of embryos.  Patient age was examined for congruency between the groups and no difference was found.  Aggregate data was analyzed and a p-value < 0.05 was defined as statistically significant, with a 95% confidence interval.

Results: No significant difference was seen between group A and group B for +HCG (64.6% vs 62.2%, p=0.535) or CIG (46.6% vs 45.2%, p=0.710).  There was a significant difference when comparing group A and group C for +HCG (64.6% vs 46.0%, p=0.0002) and CIG (46.6% vs 28.3%, p=0.0003).  There was also a significant difference when comparing group B and group C for +HCG (62.2% vs 46.0%, p=0.0054) and CIG (45.2% vs 28.3%, p=0.0032).

Conclusion: When the embryo was not fully hatched, a negative impact on pregnancy rates was not seen if the ICM was positioned outside the zona.  A significant difference in pregnancy rate was only seen if the embryo was fully hatched out of the ZP.  If an embryo is not fully hatched, the ICM position inside or outside of the ZP does not predict the likelihood of pregnancy from a single embryo PGT-A euploid frozen embryo transfers.

Disclosures: None.

Funding: None.

Poster