Impact of smoking exposure change on infant birth weight among a cohort of women in a prenatal smoking cessation study.

INTRODUCTION

Despite the known harmful effects of smoking during pregnancy, the highly addicted find it difficult to quit. Decreased smoking may be regarded as a means of harm reduction. There is limited information on the benefits of smoking reduction short of quitting. This study used salivary cotinine to assess the impact of change in smoking exposure on birth weight in full-term infants.

METHODS

In a prenatal smoking cessation study, smoking status was validated by saliva cotinine at baseline and end of pregnancy (EOP). Salivary cotinine ≥15 ng/ml defined active smoking. Based on salivary cotinine, women were grouped as nonsmoking/quit, light exposure (<150 ng/ml), and heavy exposure (≥150 ng/ml) at baseline and EOP. EOP and baseline smoking status were stratified to form smoking exposure change groups. Mean birth weight was compared among those who quit, reduced, maintained, and increased.

RESULTS

Smoking cessation was associated with a 299 g increase in birth weight compared with sustained heavy smoking, p = .021. Reduced exposure from heavy to light was associated with a 199 g increase in birth weight compared with sustained heavy exposure, a 103 g increase compared with increased exposure, and a 63 g increase compared with sustained light exposure. Differences among continuing smokers were not statistically significant.

CONCLUSIONS

Although not statistically significant, the increase in infant birth weight associated with reduction from heavy to light exposure suggests potential for benefit. The only statistically significant comparison was between quitters and sustained heavy smokers, confirming that smoking cessation should remain the goal for pregnant women.