Dose-response relationship between early pregnancy blood pressure and gestational diabetes mellitus based on propensity score matching: a retrospective study

Abstract Background Gestational diabetes mellitus (GDM) is a common pregnancy complication with substantial short- and long-term consequences for mothers and offspring. Whether modest elevations in blood pressure (BP) during early pregnancy are associated with GDM risk, particularly in a dose-response fashion, remains unclear. We examined the association between early pregnancy BP and GDM in a Chinese community-based cohort using propensity score matching (PSM) and restricted cubic spline (RCS) analyses. Methods This retrospective study included 11,338 pregnant women who registered for antenatal care in 2020 at eight community health service centers in Linping District, Hangzhou. All women underwent a 75 g oral glucose tolerance test at 24–28 gestational weeks and were classified as having GDM (n = 1,212) or not according to the International Association of Diabetes and Pregnancy Study Groups criteria. Early pregnancy BP, measured at the first antenatal visit (< 13 gestational weeks), was categorized into low, normal and high groups based on the 10th and 90th percentiles of the BP distribution. PSM (1:3 nearest-neighbor matching without replacement, caliper 0.2) was applied to balance gestational age at registration, residence, parity and cesarean section history between GDM and non-GDM groups. Conditional logistic regression and RCS models were then used in the matched cohort to estimate odds ratios (ORs) and characterize dose-response relationships between systolic BP (SBP), diastolic BP (DBP) and GDM risk. Results Overall, 1,212 (10.69%) women developed GDM. PSM yielded a matched cohort of 1,212 women with GDM and 3,636 without GDM, with all standardized mean differences for matching covariates below 0.10, indicating excellent baseline balance. In this emulated case-control setting, conditional logistic regression further adjusted for maternal age, early pregnancy body mass index and number of previous abortions showed that women in the high BP group had more than twice the odds of GDM compared with those in the low BP group (adjusted OR = 2.14, 95% confidence interval CI: 1.26–3.63). RCS analyses revealed a linear dose-response relationship between SBP and GDM (P-overall < 0.001, P-nonlinear = 0.232), with the odds of GDM increasing by 10% for every 10 mmHg increase in SBP (OR per 10 mmHg = 1.10, 95% CI: 1.03–1.17), and a nonlinear association for DBP (P-overall < 0.001, P-nonlinear = 0.008), with risk rising when DBP exceeded 80 mmHg. Associations were broadly consistent across all subgroups. Conclusions Elevated BP in early pregnancy is independently associated with an increased risk of GDM. By combining PSM with RCS modeling, this study demonstrates that even modest BP elevations, including values near the conventionally normal range, are linked to higher GDM risk. Early pregnancy BP may therefore serve as a simple, routinely available marker for identifying women at high risk and informing early prevention strategies for GDM.