Implantation in single euploid embryo transfers the role of blastocyst expansion grade and early serum -hCG levels

Objective: Is there an association between blastocyst expansion grade and early serum β-hCG levels in pregnancies after single euploid embryo transfer?

Methods: This retrospective cohort study included 8394 SEETs performed at a single center. Blastocysts were categorized as CHBs (n = 1677) or PHBs (n = 4612) based on their expansion grade. Serum β-hCG levels were measured on days 9 and 11 post-transfer. A multivariate logistic regression model adjusted for confounders, including maternal age, ovarian reserve, embryo morphology, year of treatment, and day of biopsy.

Results: On day 9 post-transfer, the median β-hCG level was significantly lower in CHBs (118 mIU/mL, IQR = 129.2) compared to PHBs (133 mIU/mL, IQR = 129.8; p < 0.0001). The difference persisted on day 11 post-transfer (CHBs: 290.2 mIU/mL, IQR = 357 vs. PHBs: 327.3 mIU/mL, IQR 358.6; p = 0.018). In multivariate regression, CHB status remained
significantly associated with lower β-hCG on day 9 post-transfer (aOR = 0.998, 95% CI: 0.997–0.999), but not on day 11 post-transfer (aOR = 0.999, 95% CI: 0.999–1.0002).

Conclusions: Completely hatched blastocysts (CHBs) with an expansion grade 6 were associated with lower early serum β-hCG levels compared to partially hatched blastocysts (PHBs) with expansion grades 4 and 5. Incorporating expansion grade into prediction models could enhance decision support tools for IVF patients.