Fetal behaviour does not differ between boys and girls P.G. Robles de Medina a , G.H.A. Visser a , A.C. Huizink b , J.K. Buitelaar b , E.J.H. Mulder a, * a Department of Perinatology and Gynaecology, Wilhelmina Children’s Hospital, KE.04.123.1, Lundlaan 6, 3584 EA Utrecht, The Netherlands b Department of Child and Adolescent Psychiatry, University Medical Centre Utrecht, Utrecht, The Netherlands Accepted 20 March 2003 Abstract 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 TimeÂSex 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. D 2003 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Fetal behaviour; General movements; Sex differences 1. Introduction Differences between men and women comprise many areas as diverse as physical appearance, brain morphology, heart rate, onset of puberty, aggression, emotional 0378-3782/03/$ - see front matter D 2003 Elsevier Science Ireland Ltd. All rights reserved. doi:10.1016/S0378-3782(03)00047-1 * Corresponding author. Tel.: +31-30-2507547/2504913; fax: +31-30-2505320. E-mail address: emulder@azu.nl (E.J.H. Mulder). www.elsevier.com/locate/earlhumdev Early Human Development 73 (2003) 17 – 26