Maternal Smokeless Tobacco Use in Pregnancy and Adverse Health Outcomes in Newborns: A Systematic Review.

Background: Perinatal morbidity and mortality are important indicators of maternal health and the future health of the child. Smokeless tobacco (ST) use during pregnancy is associated with low birth weight (LBW), preterm births, stillbirths, and small for gestation age (SGA). This study systematically reviews and summarizes evidence on the association of maternal ST use with these adverse health outcomes in newborns.

Methods: Electronic databases (Medline, Embase, Lilacs) were searched in July 2013 using appropriate keywords complemented with reference list searching. Observational studies of maternal ST use and these outcomes were considered; LBW, preterm, stillbirth, SGA. A comprehensive assessment of quality and risk of bias in all included studies was performed. RevMan software was used for data analysis. Results are expressed as crude odds ratios with 95% confidence intervals. Chi-square and I(2) tests checked for heterogeneity and quantified inconsistency between results.

Results: There were 9 studies (16 reports) included (7 cohort-studies, 1 case-control study, and 1 cross-sectional study). They were clinically and methodologically diverse. Significant associations with ST use were seen in 5/7 studies for LBW, in 3/6 studies for preterm, in all 4 studies for stillbirth and in 1/2 studies assessing SGA. Heterogeneity between results was moderate for LBW (I(2) = 44%) and stillbirth (I(2) = 52%), and high for preterm (I(2) = 87%) and SGA (I(2) = 65%). Meta-analysis was considered inappropriate due to risk of bias and confounding.

Conclusions: Although most studies show an association between ST use in pregnancy and adverse health effects in newborns, these results may be limited by confounding and bias. Quality observational studies are needed to strengthen this evidence base.