Ambulatory blood pressure in pregnancy and fetal growth

Background Retarded growth in utero has been linked with high blood pressure and other risk factors for cardiovascular disease in adult life. However, the influence on fetal growth of the maternal blood pressure during pregnancy is not well defined. In a prospective study, we examined the relation between maternal ambulatory blood pressure during pregnancy and indices of fetal growth. Methods We studied 209 healthy nulliparous pregnant women referred to an inner-city district general hospital (86% of 244 consecutively referred women who met the study criteria). 24 h ambulatory blood-pressure recordings were obtained in early (median 18 weeks [IQR 17-18]) mid (28 weeks [28]), and late (36 weeks [36]) gestation. Eight infants delivered before 32 weeks' gestation were excluded from the analysis. Findings A 5 mm Hg (1 SD) increase in mean 24 h diastolic blood pressure at 28 weeks' gestation was associated with a 68 g (95% CI 3-132) decrease in birthweight; a similar change in diastolic pressure at 36 weeks' gestation was associated with a 76 g (24-129) decrease in birthweight. These associations were independent of potential confounders (maternal age, height, weight, cigarette smoking, alcohol intake, ethnic origin, pregnancy hypertension syndromes, and preterm birth). Maternal mean 24 h diastolic blood pressure at 28 weeks' gestation was also inversely associated with the infant's ponderal index at birth in multivariate analysis (p=0.06). Higher maternal ambulatory blood pressure at 28 weeks' and 36 weeks' gestation also predicted lower head circumference, although these associations were dependent on birthweight. Associations between ambulatory systolic blood pressure and indices of fetal growth were weak and inconsistent and ambulatory blood pressure at 18 weeks' gestation did not predict fetal growth. Interpretation There is a continuous inverse association between fetal growth and maternal blood pressure, throughout the range seen in normal pregnancy. Maternal blood pressure may be an important confounding factor in the reported associations between fetal growth retardation and adult hypertension and cardiovascular disease.