Is differences in embryo morphokinetic development significantly associated with human embryo sex?†

To date, very few studies have reported on the relationship between live birth gender and embryo development kinetics. This study included 1735 women undergoing in vitro fertilization or intracytoplasmic sperm injection by using a time-lapse system. Finally, a total of 228 qualified patients with 100% implantation and known live birth information were included in the analysis. There were 174 male live births and 134 female live births. The time to 3 (t3), 4 (t4), and 5 (t5) cell development of male embryos was significantly shorter/earlier than female embryos (P < 0.05). The duration of the second cell cycle (cc2) in male embryos was significantly shorter than female embryos (P = 0.002). Multivariate logistic regression showed that only t3 had a significant correlation with live birth gender; the odds ratio (OR) was 0.786, 95% confidence interval (CI) was 0.625-0.988 (P < 0.05). When morphokinetic parameters were divided into groups based on quartiles, embryos within the sex ranges were observed to have significantly different proportions of male and female live births (P < 0.05). The results showed that t3 (<14 h) was the most relevant parameter related to live birth gender (OR 2.452, 95% CI 1.071-5.612, P = 0.03). These findings support the idea that embryo morphokinetic parameters were affected by the sex of the embryo. Currently, embryologists use embryo morphokinetics to establish models of development, in order to improve accurate selection of viable embryos. Thus, this factor needs to be considered when embryologists use embryo morphokinetics to select embryos.