Effect of marijuana use in pregnancy on fetal growth.

In a prospective study of 3,857 pregnancies ending in singleton live births at Yale-New Haven Hospital, New Haven, Connecticut, in 1980-1982, 9.5% of mothers reported using marijuana (4.1% occasionally and 5.4% at least 2-3 times monthly). Among white women, regular use was associated with an increased risk of delivering a low birth weight (less than 2,500 gm) infant (odds ratio (OR) = 2.6, 95% confidence interval (CI) = 1.1-6.2) and small for gestational age infant (OR = 2.3, 95% CI = 1.3-4.1) after adjustment for other risk factors. Nonwhite marijuana users were not at further increased risk for delivering a low birth weight or small gestational age infant beyond the elevated rates of these conditions already experienced by nonwhites in general. Marijuana use was also related to preterm delivery (gestational age less than 37 weeks from last menstrual period) in white women (OR = 1.9, 95% CI = 1.0-3.9) but not nonwhite women. Occasional use was unrelated to the risk of low birth weight, small for gestational age, or preterm delivery.