Maternal cigarette smoking and placenta previa

Objective: To identify the relationship between maternal cigarette smoking and ultrasound-confirmed placenta previa. Methods: A matched case-control design was used. Cases were drawn from the New England Medical Center and Cambridge Hospital from July 1992 through March 1994. Each case was delivered by cesarean after 24 weeks' gestation and had an antenatal ultrasound examination confirming placenta previa. Matched controls were obtained by requesting records on the first three deliveries by the referring provider the same month as the index case. Data on potential risk factors were drawn from the records of the initial prenatal visit, before previa was diagnosed. The data were analyzed with conditional logistic regression. Results: Thirty-two cases of ultrasound-documented placenta previa were identified. A number of potential confounders were associated with previa: age (odds ratio [OR] 1.15, 95% confidence interval [CI] 1.05-1.26), gravidity (OR 1.4, 95% CI 1.1-1.7), parity (OR 1.4, 95% CI 1.1-1.9), prior spontaneous abortion (OR 3.1, 95% CI 1.3-7.4), prior elective abortion (OR 3.0, 95% CI 1.2-7.6), and prior cesarean delivery (OR 3.5, 95% CT 1.3-9.9). The crude OR for current smoking was 3.0 (95% CI 1.1-8.6). The OR for smoking ranged from 2.6-4.4, despite controlling for confounders. Conclusion: Current cigarette smoking is associated with a 2.6-4.4-fold increased risk of placenta previa.