Smoking during pregnancy: the dose dependence of birthweight deficits

Abstract

Objective To assess whether a simple urine based estimate of relative daily nicotine intake could predict smoking related birthweight deficits more accurately than self‐reported cigarette consumption. Design Active smokers were identified by a simple qualitative colorimetric urine test procedure and their relative nicotine intakes assessed by determining the ratios of the urinary concentrations of nicotine plus its metabolites to creatinine using automated colorimetric methods. Setting A large teaching hospital. Participants Three thousand and thirty‐eight mothers from whom smoking histories had been elicited and who gave birth to live singleton babies after 28 weeks of gestation. Main outcome measures Birthweights (adjusted for maternal weight, maternal age, baby's sex, parity and length of gestation), maternal weight gains during pregnancy and placental weights. Results The adjusted birthweight deficits of babies born to proven active smokers averaged 226 g (95 % confidence interval 194 g to 258 g), but dose dependent effects were only apparent when nicotine intake was based on urinary nicotine metabolites/creatinine ratios. Among the smokers, adjusted birthweights fell linearly with increasing nicotine intakes but gave a predicted mean birthweight for nonsmokers that was 102 g (95 % CI 50 g to 154 g) lighter than that actually found (P < 0.0001). Maternal weight gains during pregnancy were substantially reduced in smokers and correlated more closely with urinary nicotine metabolite excretions than with reported daily cigarette consumptions. Placental weights were unaffected by smoking. Conclusions There was a closer dose‐effect relationship between birthweight deficits and urinary nicotine metabolites/creatinine ratios than with self‐reported daily cigarette consumptions. The influence of nicotine exposure on birthweight appears to be biphasic, with one mechanism operating at very low levels of tobacco smoke intake and the other causing seemingly linearly related effects over the whole range of nicotine intakes of active smokers. These findings support recent evidence that passive smoking can cause substantial birthweight deficits.

Aortic intima–media thickness in nicotine-exposed rat pups during gestation and lactation period

“…A recent study reported that passive smoking was associated with reduced birth weight (by 33 g) and 22% increased risk of low birth weight and mortality [19]. Epidemiological studies have shown that the relationship between active heavy smoking and low birth weight is stronger than the passive smoking due to dose-dependent effect [5,7,11,27,37]. In our study, the mean birth weight of the pups in the nicotine A group was lower than in other groups.…”

Accelerated Metabolism of Nicotine and Cotinine in Pregnant Smokers

“…This observation has implications for the use of cotinine as a biomarker for cigarette smoking during pregnancy. Our data do not affect the validity of cotinine levels as a predictor of pregnancy outcomes, which are based on empirical observations (Mathai et al, 1990;Bardy et al, 1993;Li et al, 1993;Ellard et al, 1996). But our study does indicate that the lower cotinine levels observed in smokers during pregnancy compared with the same individuals before or after pregnancy do not necessarily reflect less smoke exposure.…”

“…Among pregnant smokers, maternal levels of cotinine correlate better with outcome measures such as birth weight than the number of cigarettes smoked per day (Haddow et al, 1987;Mathai et al, 1990;Bardy et al, 1993;Li et al, 1993;Ellard et al, 1996;Klebanoff et al, 1998;SeckerWalker et al, 1998). Recently, a study of women during pregnancy and again postpartum found that during pregnancy the median saliva cotinine concentration per cigarette was 3.5 ng/ml versus 9.9 ng/ml when not pregnant (Rebagliato et al, 1998).…”

Feedback from a point-of-care test for nicotine intake to reduce smoking during pregnancy

“…6 This, and a number of studies, have found a closer dose -e¡ect relationship between birthweight de¢cits and nicotine metabolite levels in serum and urine than with self-reported cigarette consumption. 7,8 Serum cotinine concentration at 16 weeks'gestation was also found to have a high positive predictive value for small-for-gestational age deliveries, which was double that for self-reported smoking habit and independent of associated maternal characteristics. 9 This led to the recommendation that Original Article biochemical veri¢cation of self-reported quitting is essential to the evaluation of smoking cessation interventions and may be a useful predictor of poor pregnancy outcome.…”