Introduction: Little is known about sex differences in human fetal heart and behaviour.
Patients and methods: One hundred twenty-three nulliparous healthy women carrying a male (n=56) or female (n=67) fetus participated in this study. All pregnancies remained uncomplicated and delivery was uneventful. Ultrasound observation of fetal general movements (GM) was performed for 1 h at 15-17 (T1) and 27-28 (T2) weeks of gestation and for 2 h at 37-39 weeks (T3). Fetal heart rate (FHR) monitoring occurred simultaneously with fetal ultrasound observations at T2 and T3. The incidence of GM (percentage of time), FHR and its variability, and the incidences of fetal heart rate patterns (HRP) A-D and behavioural states 1F-4F were compared between boys and girls.
Results: There were no significant differences between males and females in the distribution of HRP A-D, overall behavioural state distribution, and basal FHR, FHR variability or the presence of GM during quiet and active sleep (or during HRP A and HRP B, respectively). A TimeXSex interaction effect for GM assessed for total record length and a higher %GM in male fetuses at term age were the only significant findings. However, these observations lost statistical significance after adjustment for the effects of fetal wakefulness, which occurred to a higher extent in male than in female fetuses.
Conclusion: Our data do not provide evidence for a difference in fetal functional development or maturation between the two sexes.