Sex differences in fetal Doppler parameters during gestation

Abstract

Background: Fetal sex is known to affect pregnancy outcomes. In current clinical practice, monitoring of fetal well-being is based on Doppler ultrasound measurements of major placental and fetal vessels. The objective of this study was to investigate the effect of fetal sex on Doppler parameters throughout gestation in healthy pregnancy.

Methods: A prospective study was conducted in 240 pregnant women with ultrasound examinations at a 4-weekly interval between 12 and 38 weeks of gestation. Pulsed Doppler spectra were collected for the umbilical arteries (UAs), middle cerebral artery (MCA), descending abdominal aorta (DAo), and ductus venosus (DV). Linear mixed effects models were used to determine if the pulsatility indices (PIs) of these vessels depended on gestational age and fetal sex.

Results: While there were no differences in the MCA PI and DV PIV over gestation between female and male fetuses, the trajectory of the UA and DAo PIs differed by fetal sex (p = 0.02 and p = 0.01, respectively).

Conclusions: Doppler ultrasound parameters were found to be dependent on fetal sex for some vessels and not for others in healthy pregnancies. Further investigations are needed to understand the physiological mechanisms for these sex differences and the relevance for disease processes in pregnancy.

Keywords: Doppler ultrasound; Fetal sex; Pregnancy; Pulsatility index; Sex differences.

Fig. 1

Sex differences in a umbilical artery pulsatility index, b middle cerebral artery pulsatility index, c descending abdominal aorta pulsatility index, and d ductus venosus pulsatility index for veins for female (red) and male (blue) fetuses. Main effect of gestational age as determined by a two-way ANOVA denoted as p_age and a significant age-by-sex interaction is denoted as p_age*sex. The shaded gray area represents 95% confidence intervals on the fitted model