Cigarette smoking and the risk of low birth weight: a comparison in black and white women. Alameda County Low Birth Weight Study Group.

With a population-based case-control study in Alameda County, we studied the difference in the risk of low birth weight in black and white smokers, the risk of preterm birth in smokers, and the time during pregnancy when smoking must cease to prevent low birth weight. The cases were 311 black and 220 white singleton low-birth-weight (500-2499 g) infants born in Alameda County in 1987. The controls were 380 black and 238 white infants of normal birth weight (greater than or equal to 3000 g) selected at random from singleton births of the same ethnicity. After adjustment for confounding, the relative risk of low birth weight in black smokers relative to nonsmokers of the same race was 3.6 (95% CI = 2.4-5.6); in white smokers it was 3.0 (95% CI = 1.7-5.3). The relative risk of term low birth weight (intrauterine growth retardation) was 4.5 in black smokers (95% CI = 2.5-8.1); in white smokers it was 5.1 (95% CI = 2.4-10.8). In both black and white women, the relative risk of two categories of preterm birth was higher in smokers than in nonsmokers. Quitting smoking in the first three months of pregnancy was associated with a lower relative risk for all categories of low birth weight in whites and for two of three categories of low birth weight in blacks. We estimate that elimination of cigarette smoking during pregnancy would prevent 18% of singleton low-birth-weight births in whites and 35% of singleton low-birth-weight births in blacks.