Dose-response relationship between maternal blood pressure in pregnancy and risk of adverse birth outcomes: Ma'anshan birth cohort study

Objectives: This study depicts the dose-response relationship between blood pressure (BP) during pregnancy and adverse birth outcomes in different trimesters. Study design: We used restricted cubic spline to quantify the dose-response relationship between maternal BP in different trimesters and risk of adverse birth outcomes (small for gestational age, SGA; and pre-term birth, PTB). The data were from the Ma'anshan birth cohort study in China (N = 3273). Main outcome measures: Risk of SGA and PTB. Results: There were dose-response associations of both systolic blood pressure (SBP) and diastolic blood pressure (DBP) with risk of SGA in the third trimester and with PTB in both second and third trimesters. In the third trimester, compared with SBP of 120 mmHg, the odds ratios (ORs) and 95% confidence intervals (CI) of SGA were 1.12 (1.01-1.19), 1.32 (1.10-1.60), 1.65 (1.20-2.27) and 2.05 (1.30-3.24) for SBP of 125, 130, 135 and 140 mmHg, respectively. The corresponding ORs and 95% CIs of PTB were 1.15 (1.00-1.32), 1.59 (1.28-1.98), 2.35 (1.66-3.33) and 3.47 (2.10-5.73), respectively. Compared with DBP of 70 mmHg, the ORs and 95% CIs of SGA were 1.44 (1.16-1.78) and 3.04 (2.06-4.50) for DBP of 80 and 90 mmHg, respectively. The corresponding ORs and 95% CIs of PTB were 1.32 (0.93-1.90) and 3.58 (2.21-5.78), respectively. Conclusions: A consistent set of dose-response relationships between maternal BP and adverse birth outcomes were observed. Most importantly, we found that moderately elevated maternal BP, even within a normal range, increased the risk of adverse birth outcomes.