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 embr yonic heart rates (EHRs) and to estimate the influence of embryonic sex on the EHR in pregnancies resulting from in vitro fertilization in the early f irst trimester. With transvaginal ultrasonography, we performed 92 and 105 examinations, on 27 male and 30 female embryos, respectively. The EHR incre ased gradually from 87 beats per min at 38 days of gestation to 189 beats p er min at 62 days of gestation. The relationship between gestational age an d EHR was explored by regression analysis: male EHR (beats per min) = 3.78 x gestational age (days) - 51.30 (r = 0.95), female EHR = 3.65 x gestationa l age - 44.56 (r = 0.95). These regression lines were mutually included in the 95% confidence intervals for each other. Our results indicate both a cl ose positive correlation between the EHR and gestational age and no statist ically significant difference in the EHR between male and female embryos. T hese findings suggest that the EHR measurement is a novel method for very e arly ultrasound dating with the identical EHR criterion without regard to e mbryonic sex.