Associations of blood pressure change in pregnancy with fetal growth and gestational age at delivery: findings from a prospective cohort

Hypertensive disorders of pregnancy are associated with intrauterine growth restriction and preterm birth. However, the associations of patterns of blood pressure change during pregnancy with these outcomes have not been studied in detail. We studied repeat antenatal blood pressure measurements of 9697 women in the Avon Longitudinal Study of Parents and Children (median [interquartile range], 10 [9-11] measurements per woman). Bivariate linear spline models were used to relate blood pressure changes to perinatal outcomes. Higher systolic, but not diastolic, blood pressure at baseline (8 weeks of gestation) and a greater increase in systolic and diastolic blood pressure between 18 and 36 weeks of gestation were associated with lower offspring birth weight and being smaller for gestational age in confounder-adjusted models. For example, the mean difference (95% confidence interval) in birth weight per 1 mm Hg/wk greater increase in systolic blood pressure between 18 and 30 weeks was -71 g (-134 to -14) and between 30 and 36 weeks was -175 g (-208 to -145). A smaller decrease in systolic and diastolic blood pressure before 18 weeks and a greater increase between 18 and 36 weeks were associated with a shorter gestation (percentage difference in gestational duration per 1 mm Hg/wk greater increase in systolic blood pressure between 18 and 30 weeks was -0.60% [-1.01 to -0.18] and between 30 and 36 weeks was -1.01% [-1.36 to -0.74]). Associations remained strong when restricting to normotensive women. We conclude that greater increases in blood pressure, from the 18-week nadir, are related to reduced fetal growth and shorter gestation even in women whose blood pressure does not cross the threshold for hypertensive disorders of pregnancy.