Increased male live-birth rates after blastocyst-stage frozen-thawed embryo transfers compared with cleavage-stage frozen-thawed embryo transfers: a SART registry study

Objective: To investigate whether there is a difference in live-birth gender rates in blastocyst-stage frozen-thawed embryo transfers (FETs) compared with those in cleavage-stage FETs. Design: Retrospective cohort study. Setting: Academic medical center. Patient(s): All women with recorded live births who underwent FET at either the blastocyst or cleavage stage, reported to the Society for Assisted Reproductive Technology during 2004–2013. Intervention(s): None. Main Outcome Measure(s): The primary outcome was live-birth gender rates. Demographic criteria were also collected. The chi-square analyses were used for bivariate associations, and multiple logistic regression models were used for adjusted associations, with all two-sided P<.05 considered statistically significant. Result(s): A statistically significant increase was noted in the number of live male births after blastocyst-stage FET compared with that after cleavage-stage FET (51.9% vs. 50.5%). After controlling for potential confounders including age (odds ratio [OR], 1.06; 95% confidence interval [CI], 1.03, 1.08), body mass index (OR, 1.08; 95% CI, 1.04, 1.12), and male factor infertility (OR, 1.06; 95% CI, 1.03, 1.08), the increase in male live births after blastocyst-stage FET remained statistically significant. Conclusion(s): In patients undergoing FETs, blastocyst-stage transfers are associated with higher male gender live-birth rates compared with cleavage-stage transfers.