We examined the risk of uteroplacental disorders in relation to cigarette smoking. Relative risks (with 95 percent confidence intervals) were computed as the measure of effect. All analyses related to smoking were performed by three methods. First, smoking was categorized as a dichotomous variable (yes/no). Second, the number of cigarettes smoked per day was treated as an ordinal variable to assess the dose response relation between the number of cigarettes smoked and the risk of uteroplacental bleeding disorders. For this analysis, number of cigarettes smoked daily was categorized as none, 1-5, 6-10, 11-15,
16-20, 21-30, and 31 or more. Third, the number of cigarettes smoked per day was modeled as a continuous variable.