Morning Blood Pressure and Adverse Pregnancy Outcomes in High-Risk Pregnancies

The association between maternal morning blood pressure (BP) levels and adverse pregnancy outcomes (APOs), including severe preeclampsia, target organ damage, preterm birth, placental abruption, postpartum hemorrhage, small-for-gestational-age infants, and pregnancy loss, is not well understood. In a retrospective cohort study of 1833 high-risk singleton pregnancies with outpatient ambulatory BP monitoring, 26.7% had morning hypertension. Morning BP strongly correlated with non-morning daytime BP (Pearson r = 0.89) and nighttime BP (r = 0.78), but only moderately with office BP (r = 0.54). Compared to office BP, adding morning BP improved diagnostic accuracy for nighttime, masked, and non-morning daytime hypertension (Δ area under the curve 0.062 to 0.127, all P < 0.001). A J-shaped, non-linear association was observed between morning BP and the risk of composite APOs, with identified thresholds at systolic/diastolic BP ≥ 132/79 mmHg. Isolated morning hypertension, compared to isolated nighttime or non-morning daytime hypertension, did not independently increase composite APO risk. However, co-occurrence of morning hypertension with nighttime (odds ratio [OR] 3.16, 95% confidence interval [CI]: 2.34 to 4.27) or non-morning daytime (OR 3.41, 95% CI: 2.54 to 4.60) hypertension amplified the risks for APOs. The strongest association between co-occurring morning and nighttime hypertension and APO risk was observed between 28⁺⁶ and 34⁺⁶ weeks of gestation (OR 5.50, 95% CI: 2.13 to 7.43). Sensitivity analyses with alternative morning time windows and adjustments for non-morning mean arterial pressure consistently confirmed these findings. Our findings support morning BP measurement as a valuable and practical marker for screening and identifying high-risk BP patterns during pregnancy.