Blood pressure trajectories during pregnancy, labor, and postpartum period: a multicenter study in Japan.

In this study, we characterized the physiological blood pressure (BP) trajectories from an estimated pre-pregnancy period through pregnancy, labor, and postpartum among low-risk, normotensive women. This retrospective multicenter observational study was conducted at 12 primary obstetric care facilities in Japan and included 14,240 low-risk, normotensive women with term singleton deliveries between 2011 and 2018. Longitudinal outpatient BP trajectories during pregnancy and the postpartum period were modeled using linear mixed-effects models with restricted cubic splines. The pre-pregnancy BP was approximated using 1:1 matching with non-pregnant women undergoing routine health checkups. Changes in intrapartum BP were evaluated in women who underwent vaginal delivery (n = 11,836). The outpatient BP followed a classic gestational pattern, with a nadir at approximately 25 weeks of gestation, followed by a gradual increase toward term. The estimated pre-pregnancy BP was lower than the outpatient BP measured during early pregnancy. During the first stage of labor, systolic and diastolic BPs increased by up to 15.7 mmHg and 13.4 mmHg, respectively, compared with the final outpatient measurements, returning to near-outpatient levels within 2 h after delivery. During the postpartum period, the BP increased, peaked at days 5-7, and then gradually declined by approximately 5 weeks, converging toward non-pregnant levels. Low-risk normotensive women demonstrated elevated BP in early pregnancy relative to the estimated non-pregnant baseline during labor and in the first postpartum week. These data provide physiological reference patterns that may aid the interpretation of intrapartum and postpartum hypertension.