Effect of Blastocyst Quality on Human Sex Ratio at Birth in Single Blastocyst Frozen Thawed Embryo Transfer Cycle

Abstract ObjectiveThis study aimed to determine whether blastocyst quality affect on sex ratio at birth through in single blastocyst frozen thawed embryo transfer cycle.Materials and MethodsWe ran this retrospective study on 4205 singleton infants born following single blastocyst frozen thawed embryo transfer from January 2016 to October 2020 at a single institution. We compared the sex ratios of these infants with respect to blastocyst quality, embryo growth rate and morphology.ResultsThe main outcomes of this study were that the sex ratio at birth of single blastocyst frozen thawed embryo transfer babies was 56.67% which was higher than the normal level (51.22%). The sex ratio of mothers older than 40 years was significantly lower than that of mothers younger than 40 years (0.39vs1.3, P<0.05). Transplanting good quality blastocysts significantly increased the proportion of boys (1.35vs0.94, P<0.05). Transplanting grade 5 and 6 blastocysts significantly increased the proportion of male babies born compared with grade 3 and 4 blastocysts (1.91vs1.28, P<0.05). There were no significant differences in the sex ratio with respect to the inner cell mass (ICM) score. In addition, the higher the trophectoderm (TE) score, the higher the sex ratio (2.79vs1.18vs0.91, P<0.05).ConclusionsOur study indicated that blastocyst quality, especially trophoblastic cell score, had a significant effect on sex ratio.