OBJECTIVETo examine the relationship between prepregnancy body mass index (BMI) and the risk of pregnancy-induced hypertension (PIH) in Chinese population.

METHODSData were collected in 6 counties/cities covered by Perinatal Health Care Surveillance System which was part of the Sino-American cooperative project on neural tube defects prevention established in 1992. The study population consisted of 83 159 women who attended premarital or preconception medical physical examination and delivered single live births with at least 20 gestational weeks from 1995 to 2000 in Jiaxing area. The Chi-square test was employed to test the difference in the rates of PIH among groups with different BMI. Multivariate logistic regression was conducted to examine the association between prepregnancy BMI and the risk of PIH.

RESULTSThe rate of PIH was 11.01% (9153/83 159; 95% CI: 10.79% - 11.22%). The rate of PIH among women with BMI < 18.5 kg/m(2), 18.5 - 22.9 kg/m(2), 23.0 - 24.9 kg/m(2), and > or = 25.0 kg/m(2) were 9.08% (1405/15 472; 95% CI: 8.63% - 9.54%), 10.82% (6389/59 054; 95% CI: 10.57% - 11.07%), 14.63% (943/6444; 95% CI: 13.78% - 15.52%), and 19.00% (416/2189; 95% CI: 17.38% - 20.71%), respectively, the difference was significant (chi(trend)(2) = 261.028, P = 0.000). Taking those with BMI 18.5 - 22.9 kg/m(2) as reference, the unadjusted RR for PIH was 0.82 (95% CI: 0.77 - 0.87) among women with BMI < 18.5 kg/m(2), 1.41 (95% CI: 1.31 - 1.52) among women with BMI 23.0 - 24.9 kg/m(2), and 1.93 (95% CI: 1.73 - 2.16) among women with BMI > or = 25.0 kg/m(2). After controlling for area, maternal age at delivery, educational level, occupation, parity, times of prenatal visit as well as the individual or family history of chronic hypertension, the estimated RR were 0.85 (95% CI: 0.80 - 0.90), 1.37 (95% CI: 1.27 - 1.47) and 1.88 (95% CI: 1.68 - 2.10), respectively.

CONCLUSIONHigh prepregnancy BMI could increase the risk of PIH.