Research question: To determine whether blastocyst quality affects the sex ratio at birth through a single blastocyst frozen - thawed embryo transfer (SBFET) cycle.
Design: In this retrospective analysis, we examined 3,041 singleton infants born following SBFET between 2017 and 2020 at a single institution. We compared the sex ratios of these infants with respect to the blastocyst quality, embryo growth rate, and morphology.
Results: The main outcomes of this study were that the sex ratio (M/F) at birth of SBFET was 1.24. Mothers >40 years old had a considerably lower sex ratio than mothers <40 years old (0.39 vs. 1.23-1.28, p < .05). Transplanting high-quality blastocysts significantly increased the proportion of boys born (1.29 vs. 0.88, p < .05). There were no significant differences in the sex ratio with respect to the inner cell mass (ICM) score and expansion degree. Additionally, a high trophoblastic cell (TE) score resulted in a significantly higher sex ratio than the TE score with C (1.62 vs. 1.15 vs. 0.85, p < .001). Multivariable logistic regression analysis was performed to determine which variables were significant factors affecting sex ratio, and the outcomes were consistent with previous findings.
Conclusions: Our study indicated that high-quality, especially good TE score, had a higher chance of resulting in a male infant than a female infant.
Keywords: Secondary sex ratio; blastocyst quality; inner cell mass; single blastocyst frozen thawed embryo transfer; trophectoderm.