Foetal sex and nonstress test characteristics

Male foetuses have historically been perceived as more active than females, and foetal movement has been observed to be greater in male foetuses in late pregnancy. Nonstress tests (NSTs), a common form of antepartum assessment, rely on movement in their interpretation. To see if this difference could influence their interpretation, NSTs of patients undergoing clinically indicated testing at 36 weeks' gestation were evaluated. In this cross-sectional observational study, tests were compared between male and female foetuses for maternal indicators of foetal movement and heart rate characteristics including baseline, variability, and number of accelerations. Among 287 foetuses analysed, recordings of foetal movement and heart rate characteristics were similar between the two groups. The results suggest no difference in movement or NST parameters between males and females, and foetal sex should not affect NST interpretation.