Female and male human embryo growth rates are similar before the eight-cell stage, ,

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 transfer: ≤3, 4, and ≥5 blastomeres. RESULTS: Percentages of girls and boys remained roughly unaltered irrespective of the number of blastomeres observed just before embryo transfer: ≤3 blastomeres, 45% and 55%; 4 blastomeres, 44% and 56%; and ≥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. (Am J Obstet Gynecol 1998;178:45-9.)