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Smoking habits and maternal serum alpha-fetoprotein levels during the second trimester of pregnancy.

In a prospective study the influence of cigarette smoking on maternal serum alpha-fetoprotein levels at 16 weeks gestation was examined. Significantly higher levels were found in 120 smokers compared with 138 non-smokers (median 54.0 and 44.3 micrograms/1 respectively, P less than 0.001). No difference in maternal body weight between the two groups could account for the results. The possibility of smoking-induced increased permeability of the placental barrier is discussed.