Month-wise estimates of tobacco smoking during pregnancy for the United States, 2002-2009.

The timing of prenatal exposure to tobacco cigarette smoking can be crucial for the developing fetus. Pushing the field beyond prior pregnancy trimester-focused smoking estimates, we estimated month-specific prevalence proportions for tobacco cigarette smoking among pregnant and non-pregnant women of the United States, with consideration of tobacco dependence (TD) as well. In advance, we posited that pregnancy onset might prompt smoking cessation in early months, before the end of the 1st trimester, and that TD might account for sustained smoking in later months, especially months 8-9, when there are added reasons to quit. Estimates are from the 2002-2009 National Surveys on Drug Use and Health Restricted-Data Analysis System (R-DAS), with large nationally representative samples of US civilians, including 12-44 year old women (n ~ 70,000) stratified by pregnancy status and month of pregnancy, with multi-item assessment of TD as well as recently active smoking. Age was held constant via the Breslow-Day indirect standardization approach, a methodological detail of potential interest to other research teams conducting online R-DAS analyses. Among 12-44 year old women in Month 1 of pregnancy, as well as non-pregnant women, just over one in four was a recently active smoker (26-27 %), and approximately one-half of these smokers qualified as a TD case (52 %). Corresponding estimates for women in Month 3 were 17.6 % and two-thirds, respectively, lending some support for our advance hypotheses. Nonetheless, our a priori TD hypothesis about Months 8-9 seems to be contradicted: an increased concentration of TD among smokers surfaced early in pregnancy. Evidence of a possible ameliorative pregnancy effect on smoking prevalence as well as TD's effect on smoking persistence might be seen quite early in pregnancy. Substitution of a month-specific view for the traditional trimester view sheds new light on how pregnancy might shape smoking behavior before the end of trimester 1, with TD seeming to thwart a public health goal of 100 % cessation, early in pregnancy.