Does a non-dipping heart rate profile predict adverse maternal–fetal outcomes? evidence from 24-h ambulatory monitoring in the second half of high-risk pregnancies

Hypertensive disorders of pregnancy are a leading cause of maternal–fetal morbidity and mortality, with preeclampsia representing a major contributor to adverse outcomes. Ambulatory blood pressure monitoring (ABPM) has improved risk stratification by identifying blood pressure phenotypes, particularly nocturnal hypertension. Given the shared autonomic mechanisms underlying nocturnal blood pressure elevation, a non-dipping heart rate pattern may theoretically provide additional prognostic information. We conducted a retrospective cohort study of 1336 high-risk pregnant women evaluated between 20 and 34 weeks of gestation using 24-h ABPM. Heart rate dipping was defined as a nocturnal reduction ≥10% compared with daytime values. Maternal and fetal outcomes included preeclampsia/eclampsia/HELLP syndrome, preterm birth, and low birth weight. A non-dipping heart rate pattern was observed in 39% of participants and was associated with higher office and ambulatory blood pressure levels and less favorable clinical profiles. Although non-dippers exhibited a higher absolute risk of adverse outcomes in unadjusted analyses, these associations were no longer significant after adjustment for established clinical risk factors and office blood pressure. Models incorporating ambulatory blood pressure averages showed substantial multicollinearity and did not support an independent prognostic role of heart rate non-dipping. Sensitivity analyses excluding women treated with beta-blockers yielded consistent results. In high-risk pregnancies, a non-dipping heart rate pattern assessed by ABPM reflects underlying blood pressure abnormalities but does not independently predict adverse maternal–fetal outcomes beyond conventional clinical and blood pressure parameters.