Development and sexual difference in embryonic heart rates in pregnancies resulting from in vitro fertilization.

The purpose of this study was to investigate the gestational change of embryonic heart rates (EHRs) and to estimate the influence of embryonic sex on the EHR in pregnancies resulting from in vitro fertilization in the early first trimester. With transvaginal ultrasonography, we performed 92 and 105 examinations, on 27 male and 30 female embryos, respectively. The EHR increased gradually from 87 beats per min at 38 days of gestation to 189 beats per min at 62 days of gestation.