Gestational ages-specific blood pressure patterns and risk of adverse pregnancy outcomes in women with chronic hypertension.

Management of chronic hypertension in pregnancy remains uncertain, and current guidelines do not address whether the prognostic significance of blood pressure (BP) varies across gestation. To evaluate gestational age-specific associations between maternal BP in the first half of pregnancy and adverse maternal and neonatal outcomes. We conducted a multicenter registry-based cohort study from April 2022 to March 2023 at 65 tertiary referral centers in Japan. A total of 273 women with chronic hypertension and singleton pregnancies were enrolled before 14 weeks' gestation (median age, 37 years; IQR, 34-40). Systolic and diastolic BP were assessed at three gestational windows (8-9, 10-13, and 14-18 weeks). Aspirin exposure was treated as time-dependent. The primary outcome was a composite of adverse maternal and neonatal events. Cox proportional hazards models and restricted cubic spline analyses were used. Adverse outcomes occurred in 32.6% (89/273). BP-risk associations differed by timing. No association was observed at 8-9 weeks. At 10-13 weeks, risk increased progressively with higher systolic BP, including excess risk in the moderate range (120-134 mmHg) and the highest risk at ≥135 mmHg (HR, 4.11; 95% CI, 1.14-14.82). At 14-18 weeks, a threshold pattern emerged, with increased risk above 140 mmHg (HR, 2.19; 95% CI, 1.40-3.43). Associations were weaker among women who initiated aspirin before 10 weeks, although interaction was not statistically significant. In chronic hypertension, maternal BP during 10-13 weeks of gestation carries heightened prognostic relevance. These findings support gestational age-specific risk assessment and motivate evaluation of early preventive strategies.