Effects of nulliparity, maternal age, and pre-pregnancy body mass index on the development of gestational hypertension and preeclampsia

Aims: We aimed to determine the effects of nulliparity, maternal age, and pre-pregnancy body mass index (BMI, kg/m(2)) on the development of pregnancy induced hypertension (PIH) in Japanese women, including gestational hypertension (GH) and preeclampsia (PE). Methods: Data on 138,530 women with singleton pregnancies who were registered with the Japan Society of Obstetrics and Gynecology and gave birth at >= 22 weeks of gestation during the three years from 2007 and 2009 were analyzed. Results: PIH was diagnosed in 6,578 (4.7%) women, including 3,326 (2.4%) with GH and 3,252 (2.3%) with PE. PIH was more frequent in nulliparous than multiparous women (relative risk [95% confidence interval], 1.30 [1.24 to 1.37]) and increased linearly with advancing maternal age after 35 years and also with increasing pre-pregnancy BMI. PIH also varied greatly among 24 groups stratified according to 4 maternal age categories and 6 pre-pregnancy BMI categories, with the lowest frequency (2.7%) among lean (BMI < 18.5) women 20-34 years of age and the highest frequency (21.7%) among obese (BMI >= 30) women >= 40 years of age. Conclusions: Our findings provide useful information for counseling Japanese women about the risk of PIH at the beginning of pregnancy.