Blood pressure trajectory and category and risk of hypertensive disorders of pregnancy in nulliparous women.

Background: Recently updated American College of Cardiology/ American Heart Association (ACC/AHA) guidelines redefine blood pressure categories as stage 1 hypertension (systolic, 130-139 mm Hg or diastolic, 80-89 mm Hg), elevated (systolic, 120-129 mm Hg and diastolic, <80 mm Hg), and normal (<120/<80 mm Hg), but their relevance to an obstetric population is uncertain.

Objective: We sought to evaluate the risk of gestational hypertension or preeclampsia based on early pregnancy blood pressure category and trajectory.

Study Design: We utilized data from the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-Be cohort, a prospective observational study of nulliparous women with singleton pregnancies conducted at 8 clinical sites between 2010 and 2014. Women included in this analysis had no known history of prepregnancy hypertension (blood pressure, ≥140/90 mm Hg) or diabetes. We compared the frequency of hypertensive disorders of pregnancy, including preeclampsia and gestational hypertension, among women based on ACC/AHA blood pressure category at a first-trimester study visit and blood pressure trajectory between study visits in the first and second trimesters. Blood pressure trajectories were categorized based on blood pressure difference between visits 1 and 2 as stable (<5 mm Hg difference), upward (≥5 mm Hg), or downward (≤-5 mm Hg). Associations of blood pressure category and trajectory with preeclampsia and gestational hypertension were assessed via univariate analysis and multinomial logistic regression analysis with covariates identified a priori.

Results: A total of 8899 women were included in the analysis. Study visit 1 occurred at a mean gestational age of 11.6 ± 1.5 weeks and study visit 2 at a mean gestational age of 19.0 ± 1.6 weeks. First-trimester blood pressure category was significantly associated with both preeclampsia and gestational hypertension, with increasing blood pressure category associated with a higher risk of all hypertensive disorders of pregnancy. Elevated blood pressure was associated with an adjusted relative risk of 1.54 (95% confidence interval, 1.18-2.02) and stage 1 hypertension was associated with adjusted relative risk of 2.16 (95% confidence interval, 1.31-3.57) of any hypertensive disorder of pregnancy. Stage 1 hypertension was associated with the highest risk of preeclampsia with severe features, with an adjusted relative risk of 2.48 (95% confidence interval, 1.38-8.74). Both systolic and diastolic blood pressure trajectories were also significantly associated with the risk of hypertensive disorders of pregnancy independent of blood pressure category (P < .001). Women with a blood pressure categorized as normal and with an upward systolic trajectory had a 41% increased risk of any hypertensive disorder of pregnancy (adjusted relative risk, 1.41; 95% confidence interval, 1.20-1.65) compared to women with a downward systolic trajectory.

Conclusion: In nulliparous women, blood pressure category and trajectory in early pregnancy are independently associated with risk of preeclampsia and gestational hypertension. Our study demonstrates that blood pressure categories with lower thresholds than those traditionally used to identify individuals as hypertensive may identify more women at risk for preeclampsia and gestational hypertension.