Peacock, Janet L., Cook, Derek G., Carey, Iain M., Jarvis, Martin J., Bryant, Andrew E., Anderson, H. Ross and Bland, J. Martin
Maternal cotinine level during pregnancy and birthweight for gestational age.
International Journal of Epidemiology, 27, (4), .
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Background Recent studies have found that cotinine is a better predictor of birthweight than
the number of cigarettes smoked in pregnancy. In this paper we test this hypothesis
and use cotinine to explore the effect of environmental tobacco smoke
(ETS) on birthweight.
Methods In all, 1254 white women were interviewed at booking, 28 and 36 weeks about
the number and brand of cigarette smoked. Cotinine was assayed from blood
samples taken on the day of interview. The outcome was birthweight for gestational
Results There was good agreement between self-reported smoker/non-smoker status and
maternal cotinine with 1.3% women mis-reported as non-smokers at booking,
0.6% and 1.8% mis-reported at 28 and 36 weeks respectively. Among smokers,
cotinine was more closely related to birthweight than the number of cigarettes
smoked at all three time points (r = -0.25 versus r = -0.16 at booking). A reduction
in cotinine between booking and 28 weeks was associated with increased
birthweight but the effect was not statistically significant. Among non-smokers
the association between birthweight and cotinine was not statistically significant
after adjusting for maternal height, parity, sex and gestational age. Difference in
mean birthweight between non-smokers in the lower and upper quintiles of
cotinine was 0.2% (95% CI: -2.4, 2.8). Pooling the results of 10 studies plus our
own gave an estimated difference in mean birthweight between women
unexposed and exposed to passive smoke of 31 g (95% CI: 19, 44).
Conclusions Cotinine is a better predictor of birthweight than the reported number of cigarettes
smoked. If biochemical analysis is impossible, then self-reported smoking
habit should be obtained prospectively using a structured approach. Any effect on
birthweight of maternal passive smoking during pregnancy is small compared
with the effects of maternal active smoking.
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