Cumulative and residual risks of small for gestational age neonates after changing pregnancy-smoking behaviors

This retrospective cohort study examines the relationship between changing pregnancy-smoking behaviors, from the first to the second pregnancy, on second-pregnancy rates of small for gestational age (SGA) neonates. Electronic birth records provided data on 5107 pregnant women who had two singleton births in Kansas City, MO, from 1994 to 2003. Pregnancy-smoking behavior was classified by smoking status (nonsmoker [NS] or smoker [SMK]) during the first (previous)/second (current) pregnancy: NS/NS, NS/SMK, SMK/SMK, and SMK/NS. The overall second-pregnancy SGA rate was 6.7% and varied with pregnancy-smoking behavior: 5.9%, NS/NS; 6.6%, SMK/NS; 12.5%, NS/SMK; and 12%, SMK/SMK; P < 0.001 Current pregnancy-smoking was associated with increased odds ratio (OR) of SGA; SMK/SMK (OR, 2.80; 95% confidence interval [CI], 2.00 to 3.93) versus NS/SMK (OR, 1.83; 95% CI, 1.19 to 2.82) versus SMK/NS (OR, 1.31; 95% CI, 0.65 to 2.65) versus NS/NS (OR, 1.00; 95% CI, reference). Being black (OR, 3.73; 95% CI, 2.91 to 4.79) and having medical risk factors (OR, 1.31; 95% CI, 1.09 to 1.74) also were significantly associated with a SGA neonate in second pregnancy. In conclusion, risk of delivering a SGA neonate in a current pregnancy is related to current rather than previous pregnancy-smoking. Therefore, antismoking socialization during pregnancy should focus on preventing and stopping current pregnancy-smoking, irrespective of past behavior.