Cigarette smoking and spontaneous abortion of known karyotype. Precise data but uncertain inferences

Data from the first phase (1974-1979) of this New York City case-control study showed that 1) cigarette smoking during pregnancy was associated positively with chromosomally normal spontaneous abortion and 2) both past and current smoking were associated inversely with trisomic loss in women under age 30 years and positively in older women. The authors used data from two subsequent study phases (1979-1982 and 1982-1986) to test the stability of these associations over time and the homogeneity between payment groups (private vs. public). Spontaneous abortions (cases) were classified as chromosomally normal (n = 1,388), trisomic (n = 557), or other chromosomally aberrant (n = 409). Controls (n = 4,165) were women who had registered for prenatal care before 22 weeks' gestation and delivered at 28 weeks or later. For chromosomally normal loss, later data gave modest support to prior observations. In the total sample, current smoking (defined as smoking during the month of the last menstrual period) of 14 or more cigarettes per day was increased among chromosomally normal cases in comparison with controls (adjusted odds ratio (OR) = 1.3, 95% confidence interval (CI) 1.1-1.7) and in comparison with other aberrant cases (adjusted OR = 1.2, 95% CI 0.8-1.8). Stronger associations in public patients than in private patients (adjusted odds ratios of 1.4-1.5 versus 0.8-0.9, respectively) might indicate either a mediating effect of social disadvantage or a chance fluctuation. For trisomic loss, later data did not support prior observations. Associations between trisomy and past or current smoking did not vary significantly with age in either payment group; assuming no effect modification of age, adjusted odds ratios for smoking in relation to trisomy were 0.9-1.0.