Objective: To determine the association between pregnancy-induced hypertension(PIH) and risk of preterm delivery (PD) and low birth weight (LBW).
Methods: A prospective cohort was established based on 131 867 women who delivered a singleton baby in seven cities or counties in Zhejiang province, China, during the period of 1995 - 2000. The exposure group included 14 278 women who were diagnosed as PIH, and the non-exposure group included 117 589 women. The exposure group was divided into mild, moderate, and severe subgroups based on the severity of PIH, and further divided into early, medium and late onset subgroups based on the time of onset of PIH (occurred in second trimester, third trimester, or during delivery). The primary outcome measures were the incidence of PD and LBW. Multiple logistic regression was used to estimate relative risk and 95% confidence intervals after adjustment by maternal age, occupation, education, parity, number of prenatal visits, gestational disease, caesarean delivery, pregnant body mass index, fetal sex, and gestational age (only for LBW).
Results: The incidence rates of PD and LBW in exposure group were 4.9% (701/14 278) and 3.6% (507/14 278), and both rates were higher than those of the non-exposure group (3.4% (4031/117 589), 1.8% (2110/117 589)) (chi(2) values were 80.8 and 202.0, P < 0.001). The incidence rates of PD in mild, moderate, and severe subgroups were 3.9% (404/10 358), 5.8% (181/3099), and 14.1% (116/821), and corresponding incidence rates of LBW were 2.5% (258/10 358), 4.9% (151/3099), and 11.9% (98/821). Both rates were increased with the severity of PIH (chi(2) values were 196.4 and 426.1, P-value for trend < 0.001). The incidence rates of PD in early, medium, and late onset subgroup were 8.4% (50/598), 5.7% (278/4867), and 4.2% (373/8813), and corresponding incidence rates of LBW were 5.7% (34/598), 4.2% (206/4867), and 3.0% (267/8813). Both rates were decreased by the time of PIH onset (chi(2) values were 115.4 and 239.8, P-value for trend < 0.001).
Conclusion: PIH could increase the incidence of PD and LBW.