OBJECTIVELY MEASURED TOBACCO EXPOSURE DURING PREGNANCY - NEONATAL EFFECTS AND RELATION TO MATERNAL SMOKING

Objectives To measure quantitatively and objectively the maternal and fetal tobacco exposure during pregnancy and its neonatal effects. Desi gn Tobacco exposure was assessed from maternal serum samples, obtained during the first half of pregnancy and from umbilical serum samples o btained at delivery, by measuring the concentration of nicotine metabo lite, cotinine. Data on the respective pregnancies and neonates were c ollected from the Finnish Medical Birth Registry. Setting Finland. Sub jects One thousand two hundred and thirty-seven pregnancies and newbor ns, representing all pregnancies resulting in a liveborn infant during one week in one country. Main outcome measures Gestational age, birth weight and crown-heel length of newborns. Results Cotinine (>6 mug/l) was detected in either maternal or umbilical serum in 300 pregnancies, and these mothers and newborns were classified as exposed. Important differences occurred between measured exposure and reported smoking be haviour. Of the exposed mothers, 38% were nonsmokers and 3.4% of the n onexposed mothers were smokers. Tobacco exposure was associated with s horter gestational age, reduced birthweight and shorter crown-heel len gth of the newborns. After correction for parity, gender, and gestatio nal age, the exposed newborns were on average 188 g (95% confidence in terval (CI) 123-253 g) lighter and 10 mm (95% CI 7-13 mm) shorter than the nonexposed newborns. One mug/ml of cotinine in maternal serum res ulted in a mean decrease of 1.29 g (95% CI 0.55-2.02 g) in birthweight and in a mean decrease of 0-059 mm (95% CI 0.035-0.083 mm) in birth l ength. Maternal cotinine concentrations better explained the neonatal findings than the reported smoking habits. Conclusions There is a quan titative dose and effect relation between tobacco exposure and a decre ase in the gestational age at birth and size of the neonate. The smoki ng habit reported by mothers themselves is not an accurate measure of fetal tobacco exposure.