Preconception Blood Pressure and Adverse Pregnancy Outcomes: A Population-Based Cohort Study

Abstract

BACKGROUND: Adverse pregnancy outcomes (APOs) share clinical features and risk factors with cardiovascular disease and there is an increasing prevalence of hypertension among reproductive women. However, the associations between maternal preconception blood pressure (BP) and APOs remain controversial and inconclusive. METHODS: This population-based cohort study used data of 567 127 mother-neonate-father triads from the National Free Preconception Checkup Project in Guangdong Province, China. Maternal BP levels within 1 year before pregnancy were classified using the American College of Obstetricians and Gynecologists definition of hypertension. The primary outcome was a composite of APOs, including preterm birth, small for gestational age, and perinatal infant death. Log-binomial and marginal structural binomial regressions were employed to estimate adjusted risk ratios and absolute risk differences, respectively. RESULTS: Compared with women with normal BP, women with elevated BP (adjusted risk ratio, 1.07 [95% CI, 1.05–1.09]; absolute risk difference, 1.03% [95% CI, 0.72%–1.29%]), hypertension (adjusted risk ratio, 1.25 [95% CI, 1.18–1.32]; and absolute risk difference, 3.42% [95% CI, 1.97%–5.42%]) had a higher risk of a composite of APOs. Compared with women with normal BP, women with elevated BP and hypertension had higher risks of multiple APOs, preterm birth, small for gestational age, and perinatal infant death. However, these associations attenuated with increasing duration of pregnancy preparation and were not statistically significant beyond 90 days of pregnancy preparation. CONCLUSIONS: Women with elevated BP or hypertension before pregnancy were associated with an increased risk of APOs. Preconception hypertension screening and control among women should not be ignored by policymakers, clinicians, and the general population.