Blood pressure in early and mid-pregnancy and the risk of small-for-gestational-age birth: findings of a large cohort study in China.

The influences of blood pressure in early to mid-pregnancy on the risk of small-for-gestational-age (SGA) birth are not clear. Our objective was to examine the associations of the blood pressure levels at 10 and 18 gestational weeks with the risk of SGA birth. Data were obtained from the Chinese Maternal and Newborn's Health Monitoring System (MNHMS). In total, 50745 Chinese women who delivered a single live infant at a gestational age of between 28 and 42 weeks were included in this analysis. Blood pressure, birth outcome and other related information were obtained during antenatal visits by obstetricians. Logistic regression models were used to examine the associations, adjusting for potential confounders. The total incidence of SGA birth was 8.9%. High blood pressure levels at 10 gestational weeks significantly increased the risk of SGA birth (SBP: RR = 1.32, 95% CI: 1.11-1.56; DBP: RR = 1.10, 95% CI: 1.05-1.14). The incidence of SGA birth was not associated with the DBP at 18 gestational weeks but showed a U-shaped relationship with SBP. A decrease in blood pressure from 10 to 18 gestational weeks was associated with an increased risk of SGA birth (SBP: RR = 1.03, 95% CI: 1.00-1.07; DBP: RR = 1.05, 95% CI: 1.02-1.09). Our results provide evidence on the relationship of blood pressure in early and mid-pregnancy with SGA birth. Higher blood pressures during early pregnancy and greater decreases in blood pressure from early to mid-pregnancy increased the risk of SGA birth, indicating a continuum of risk for SGA birth based on blood pressure starting during early pregnancy.