Glucose tolerance and risk of gestational diabetes mellitus in nulliparous women who smoke during pregnancy

Gestational diabetes mellitus has been associated with adverse maternal and infant outcomes, including preeclampsia and fetal macrosomia. Although cigarette smoking has been associated with increased insulin resistance, its effect on gestational diabetes mellitus risk is uncertain. The authors evaluated the effects of smoking on glucose tolerance in a cohort of pregnant women who participated in the Calcium for Preeclampsia Prevention trial, a randomized study of nulliparous women conducted in five US medical centers from 1992 to 1995. Results of screening and diagnostic testing for gestational diabetes mellitus were analyzed. For 3,774 of the 4,589 women enrolled, plasma glucose concentration 1 hour after a 50-g oral glucose challenge and complete information on pregnancy outcome were available; for 3,602 of the women, gestational diabetes mellitus status was known. Adjusted mean 1-hour plasma glucose concentration (mg/dl) was elevated in women who smoked at study enrollment (112.6, 95% confidence interval: 110.0, 115.3) compared with women who had never smoked (108.3, 95% confidence interval: 106.7, 109.8; p < 0.01). Women who smoked were at increased risk of gestational diabetes mellitus when criteria proposed by the National Diabetes Data Group were used (adjusted odds ratio = 1.9, 95% confidence interval: 1.0, 3.6). These findings support an association between smoking and gestational diabetes mellitus.