The association between nulliparity and gestational hypertension.

The association between nulliparity and gestational hypertension was examined by analysis of the 1988 National Maternal and Infant Health Survey. Gestational hypertension was defined as the occurrence of two consecutive diastolic blood pressure readings > or = 90 mm Hg after 20 completed weeks gestation in the absence of proteinuria in subjects normotensive prior to pregnancy. Preeclampsia was defined as gestational hypertension in the presence of significant proteinuria. Using logistic regression, 110 subjects with gestational hypertension and 34 subjects with preeclampsia were compared with 4371 subjects free of all hypertensive disorders. Nulliparity was weakly associated with an increase in the risk of gestational hypertension among whites (odds ratio, 95% confidence interval: 1.58 [0.92-2.74]) and not associated with risk among blacks (1.09 [0.51-2.35]). Preeclampsia was strongly associated with increased risk among whites (2.86 [0.94-8.73]) and blacks (2.94 [0.94-9.18]). The small increase in risk of gestational hypertension associated with nulliparity in contrast with the large increase in risk of preeclampsia suggests that these disorders may have a different etiology.