Objective: Our purpose was to assess the possible relationship between human embryo growth rates and sexual differentiation.
Study design: We analyzed 142 conceptional in vitro fertilization and embryo transfer cycles undertaken in 137 women (151 embryos transferred) in which each embryo transferred led to a gestational sac. Embryos were sorted into three groups according to the number of blastomeres assessed just before embryo transfers < or = 3, 4, and > or = 5 blastomeres.
Results: Percentages of girls and boys remained roughly unaltered irrespective of the number of blastomeres observed just before embryo transfer: < or = 3 blastomeres, 45% and 55%; 4 blastomeres, 44% and 56%; and > or = 5 blastomeres, 45% and 55%, respectively (statistical power 90% at the 5% significance level).
Conclusions: This indicates that embryo growth rates before the eight-cell stage are not related to the sex of the live-born infant, thereby dissuading the use of embryo growth rates in the appraisal of sex likelihood in regular in vitro fertilization-embryo transfer.