Smoking was weakly associated with the risk of
placenta previa (table 4). When adjusted for confounding due to marital status, maternal age, parity, chronic
hypertension, preeclampsia, and alcohol use, the relative risk for placenta previa was 1.36 (95 percent CI
1.04-1.79). No dose-response gradient was observed
in relation to the number of cigarettes smoked per day.
Nevertheless, women who smoked 16-20 cigarettes
per day were at 80 percent (95 percent CI 1.06-3.07)
increased risk of placenta previa in comparison with
nonsmokers. The risk of placenta previa was slightly
elevated for women who drank alcohol during pregnancy (RR = 1.26, 95 percent CI 0.95-1.69), after
adjustment for confounders.