Leptin, a hormone produced in adipose tissue and placenta, is potentially important in relation to energy metabolism and growth. We investigated the effect of cigarette smoking on maternal plasma leptin concentration during pregnancy, and on plasma leptin concentration and weight among infants up to 13 wk of age. Plasma leptin concentration was measured in women in week 18 (n = 203) and week 35 (n = 164) of pregnancy, while cotinine (nicotine metabolite) was measured in plasma sampled from mothers in week 35 of pregnancy (n = 159). Leptin concentration was also measured in plasma from the umbilical cord (n = 133) and from 4-wk-old (n = 129) and 13-wk-old (n = 130) infants. There was no difference in plasma leptin concentration between smoking and non-smoking mothers at 18 wk and at 35 wk of pregnancy. Plasma cotinine concentration was higher in smoking than in non-smoking mothers, and a negative correlation between plasma cotinine and leptin concentrations was found. The leptin concentrations in umbilical cord plasma were similar, although the birthweights of newborns from smoking mothers were significantly lower than those from non-smoking mothers. The plasma leptin concentrations were similar between the two groups also at 4 wk of age. At 13 wk of age, infants of smoking mothers had significantly higher plasma leptin concentrations than infants of non-smoking mothers.
Conclusion: Our results indicate that a lower birthweight of neonates among smoking mothers is not due to altered plasma leptin concentration.