208: By when do I have to quit? Could I just cut down some? Evidence to help inform difficult questions in pregnancy smoking interventions

Abstract

Women who participate in pregnancy smoking interventions often do not quit smoking right away or completely. Due to the need for very large data sets, little evidence exists to inform advice about when quitting should occur, or whether a certain amount of reduction is beneficial. The goal of the current study was to examine the effect of timing of quitting and/or amount of smoking later in pregnancy on newborn birth weight, the birth outcome most often affected by smoking and highly predictive of other adverse events. Data for all births in Tennessee, a state with a high rate and amount of pregnancy smoking, were available for a three-year period and included standard birth certificate variables. Of the 241,616 women, 15.7% (n=37,975) self-reported entering pregnancy as smokers, with 20.4% (n=7,728) quitting by delivery, and another 31.7% (n=12,033) reporting smoking reduction. Compared to those who did not smoke at all, those who quit by the end of the first trimester had only a slightly increased risk of a low birth weight (LBW) delivery (OR=1.16). Overall, smoking into the second trimester but quitting prior to the third led to substantial increase in the likelihood of LBW (OR=1.70), and smoking to delivery nearly doubled the risk of LBW (OR=1.95). Several timing of quitting and amount of reduction patterns across the three trimesters were examined, with any smoking beyond the first trimester substantially increasing the risk of LBW over even smoking more than 10 cig/day in the first trimester then quitting (OR=1.30). Even smoking 5 or fewer cigarettes per day after the end of the first trimester only slightly decreased the risk of LBW compared with higher levels of smoking through to delivery (OR=.95). The self-report nature of the data poses some limitations, and other important outcomes besides LBW may reveal different results. However, these findings suggest that if the goal is to avoid a LBW delivery, pregnant smokers should be advised that quitting completely by the end of the first trimester is important, and that continuing to smoke even 5 cigarettes or fewer per day after that point substantially increases the risk that their newborn will be LBW.