The effect of tobacco exposure on maternal and fetal thyroid function

ObjectiveTo determine the effect of smoking on maternal and fetal thyroid function.Study designThis prospective cohort study involved healthy women undergoing elective cesarean section for term singleton infants. Maternal and fetal thyroid indices were compared between smokers (n = 21) and non-smokers (n = 83).ResultsMaternal thyrotropin (TSH) concentrations were significantly lower in smokers than non-smokers (1.75 mIU/L versus 2.15 mIU/L, respectively, p = 0.007), with similar free thyroxine (FT4) concentrations (9.59 pmol/L versus 9.56 pmol/L, p = 0.755). For women who smoked, the correlation between the average number of cigarettes smoked per day and maternal TSH concentrations was −0.427, p = 0.054. Infants of smokers and non-smokers had similar umbilical TSH (5.43 mIU/L versus 5.82 mIU/L, p = 0.124) and FT4 concentrations (13.06 pmol/L versus 13.57 pmol/L, p = 0.049).ConclusionWe demonstrated for the first time that women who smoke during pregnancy have significantly lower TSH concentrations than non-smokers.