Smoking before pregnancy and risk of gestational hypertension and preeclampsia.

Objective: Our purpose was to determine whether smoking before pregnancy reduces the risk of gestational hypertension or preeclampsia.

Study Design: The trial of Calcium for Preeclampsia Prevention (CPEP) was a randomized study of 4589 nulliparous women conducted in 5 US medical centers during the years 1992 through 1995. Women were classified into 4 exposure groups by smoking history obtained at study enrollment (13-21 weeks' gestation): (1) never smoked, (2) smoked but quit before the last menstrual period (LMP), (3) smoked but quit after LMP but before enrollment, and (4) smoked and still smoking at enrollment.

Results: After adjustments were made for maternal age, race, body mass index, type of health insurance, and clinical center, women smoking at enrollment had a reduced risk of hypertension (relative risk = 0.8; 95% CI, 0.6-0.9). Women who quit smoking before the LMP did not have reduced risk (relative risk = 1.1; 95% CI, 0.9-1.3). Results were similar for gestational hypertension and preeclampsia examined separately.

Conclusion: Women who smoke but quit before becoming pregnant do not have a reduced risk for gestational hypertension or preeclampsia.