FACTORS AFFECTING EMBRYO DEVELOPMENTAL PACE

Abstract

Ovarian follicle size reportedly correlates with oocyte maturity and embryo morphology. The day of blastulation (day 5, 6, or 7) has been correlated with embryo implantation potential. The objective of this study was to identify factors, including follicle diameter, that might influence the day of embryo blastulation. In this prospective observational study, patients underwent routine ovarian stimulation with exogenous gonadotropins. Each aspirated follicle was sonographically measured during oocyte collection. Embryos were cultured to the blastocyst stage. The day of blastulation was recorded for blastocysts of transferable quality (no CC grades). Blastocysts forming after day 5 were considered delayed. Logistic regressions were run to determine if patient age, follicle diameter, and the total number of eggs collected correlated with blastocyst formation on day 5. Because of the potential for biopsy to artificially influence blastulation, separate logistic regression models were developed for biopsied and non-biopsied blastocysts. P<0.05 was considered significant. The day of blastulation was recorded for 514 blastocysts derived from measured follicles, 221 of which formed on day 5, 249 on day 6, and 44 on day 7. Two logistic regression models were constructed. The first logistic model was developed predicting day 5 blastulation among the 170 biopsied blastocysts. The only significant predictor of day 5 blastulation in this model was follicle diameter (P=0.0038). The second logistic model was developed for 344 blastocysts that were not biopsied. In this second model, the only significant predictor of day 5 blastulation was, again, follicle diameter (P=0.0067). In both models, increasing follicle diameter corresponded with increased risk of delayed blastulation (day 6 or day 7 blastulation). Regardless of biopsy for PGT-A, larger follicles were significantly associated with delayed blastulation. Patient age and the number of eggs collected were not significant predictors of delayed blastulation.