Preconception Blood Pressure and Risk of Low Birth Weight and Small for Gestational Age: A Large Cohort Study in China

Our objective was to examine whether high blood pressure in the preconception period was associated with low birth weight (LBW) and small-for-gestational age (SGA) in Chinese women. Data were obtained from the China-US Collaborative Project for Neural Tube Defects Prevention, a large population-based cohort study. We included 43 718 singleton live births delivered at gestational ages of 28-45 weeks to women who were registered before pregnancy in 7 counties in southern China. Blood pressure was measured during registration by trained healthcare workers, and other health-related information was recorded prospectively. We used logistic regression to evaluate the associations between preconception blood pressure and the risk of LBW and SGA, adjusting for potential confounders. The prevalence of hypertension in the preconception study population was 4.62% (2019/43 718). The incidences of LBW and SGA were 2.33% and 5.05% for the hypertension group and 2.01% and 5.68% for the nonhypertension group. Compared with the nonhypertension group, the hypertension group did not show significantly increased risk for LBW overall (adjusted risk ratio =1.16, 95% confidence interval 0.86-1.57) or SGA (adjusted risk ratio =0.89, 95% confidence interval 0.73-1.09). When participants with normal blood pressure were used as the reference, the adjusted risk ratio of SGA for prehypertensive women was 1.13 (95% confidence interval 1.03-1.25). Our results do not support an association between hypertension or higher blood pressure before pregnancy and increased risk of LBW or SGA.