Impact of gestational hypertension and pre-eclampsia on preterm birth in China: a large prospective cohort study

OBJECTIVE: To investigate the impact of gestational hypertension and pre-eclampsia on preterm birth. DESIGN: The data were collected from the China–US Collaborative Project for Neural Tube Defect Prevention; this was a large population-based cohort study. SETTING AND PARTICIPANTS: We selected participants registered in two southern provinces, for whom we had exact information on gestational blood pressure and pregnancy outcomes, and who were not affected by chronic hypertension. In total, 200 103 participants were recruited from 1993 to 1995. OUTCOME MEASURES: Preterm birth was defined as a singleton pregnancy and birth before 37 gestational weeks. RESULTS: The incidences of gestational hypertension and pre-eclampsia were 5.47% and 5.44%, respectively, for women who gave birth at full term, and 5.63% and 7.33%, respectively, for those who gave birth preterm. After adjusting for potential confounders, the risk ratios (RRs) of preterm birth in women with gestational hypertension and pre-eclampsia were 1.04 (95% CI 0.98 to 1.11) and 1.39 (95% CI 1.25 to 1.55), respectively. The associations were stronger for early-onset (<28 weeks of gestation) gestational hypertension (adjusted RR=2.13, 95% CI 1.71 to 2.65) and pre-eclampsia (adjusted RR=8.47, 95% CI 5.59 to 12.80). CONCLUSIONS: Pre-eclampsia was associated with a higher risk of preterm birth. The early-onset gestational hypertension and pre-eclampsia were associated with more severe risks than late-onset conditions.