Elevated Pre-Pregnancy Blood Pressure and the Risk of Adverse Pregnancy Outcomes: Evidence From a Nationwide Population-Based Study

Abstract

Background: Pre-pregnancy blood pressure (BP) has gained attention as a potential predictor of adverse pregnancy outcomes. However, data on the impact of mildly elevated BP, particularly in women without overt hypertension, remain limited. In this study, we aimed to examine the association between pre-pregnancy BP and adverse pregnancy outcomes in women without a history of hypertension.

Methods: In this retrospective nationwide study, we included pregnant women with pre-pregnancy BP below 140/90 mmHg and no prior diagnosis of hypertension. Participants were categorized based on their pre-pregnancy BP into the normal BP (< 120/80 mmHg), elevated BP (120-129 and < 80 mmHg), and stage 1 hypertension (130-139 or 80-89 mmHg) groups. The following adverse pregnancy outcomes were recorded: preeclampsia, gestational diabetes, placental abruption, postpartum hemorrhage, preterm birth, and small or large for gestational age. Multivariable logistic regression was used to evaluate the associations between pre-pregnancy BP categories and adverse pregnancy outcomes.

Results: Among 298,433 women, 76.9% had normal BP, 8.7% had elevated BP, and 14.3% had stage 1 hypertension. The incidence of adverse outcomes significantly increased in groups with higher BP (normal BP, 24.8%; elevated BP, 27.1%, and stage 1 hypertension, 29.9%; P < 0.001). Compared to the normal BP group, adjusted odds ratios for adverse outcomes were 1.11 (95% confidence interval [CI], 1.07-1.14) for the elevated BP group and 1.24 (95% CI, 1.21-1.27) for the stage 1 hypertension group. A curvilinear relationship was observed between pre-pregnancy BP and the risk of adverse pregnancy outcomes.

Conclusion: Even modest increases in pre-pregnancy BP below the clinical threshold for hypertension were associated with a higher risk of adverse pregnancy outcomes. These findings highlight the need for early BP monitoring and management before pregnancy.