Smoking during pregnancy: a significant cause of neonatal thyroid enlargement

Abstract

Summary. The influence of maternal smoking during pregnancy on the function and the echographic volume of the neonatal thyroid gland was examined in an area of borderline iodine intake (median maternal urinary iodine: 315 range 79–1558 nmol/l). There was a positive correlation (P<0.001) between cord serum thiocyanate (SCN) concentrations used as an index of maternal smoking and the maternal smoking habits. The thyroid volume/birthweight ratio increased significantly as a function of SCN values (P<0.005): this increase was secondary to a decrease in birthweight as well as to an increase in thyroid volume. There was also a positive correlation between cord serum thyroglobulin (Tg) and SCN levels (P = 0.001). Serum thyroid‐stimulating hormone (TSH) and free thyroxine (FT4) values remained within the normal range for age in all newborn infants and were not significantly correlated with SCN values. These results show that smoking during pregnancy in areas with borderline iodine intake may be a significant cause of thyroid enlargement in the newborn.

Effect of passive smoking on thyroid function in infants

“…The present study confirmed the increased concentrations of cord TG in the infants of smoking parents as previously reported by Chanoine et al (5); this increase was accompanied by increased concentrations of thiocyanate in group C compared with group A. Furthermore, it seems that the exposure of the pregnant woman to passive smoking by her partner resulted in a significant passage of the metabolites of nicotine through the placenta, as group B also demonstrated increased concentrations of TG and thiocyanate in cord blood.…”

“…Among the metabolites, the influence of thiocyanate on thyroid function has received particular attention (5,15,16), both in vivo and in vitro, with conflicting results. Increased TG levels (5, 16), reduced TSH concentrations (17)(18)(19), associated unaltered (17) or increased T 4 concentrations (18), and reduced (16) or normal (19) T 3 concentrations have been reported.…”

“…In view of the significant correlation that has been reported between cord blood concentrations of thiocyanate and thyroglobulin (TG) (5), suggesting a direct effect of thiocyanate on the thyroid gland, our aim was to follow infants to 1 year of age, in order to explore the hypothesis that an altered thyroid function can persist in consequence of protracted exposure to passive smoking.…”

“…Thiocyanate, derived from hydrogen cyanide, leads to increased excretion of iodine, seems to inhibit iodine uptake by the thyroid, and can have a goitrogenic effect in the presence of iodine deficiency (5)(6)(7).…”

Effects of smoking on thyroid function

“…The infants had no other evidence of thyrotropin-independent thyroid stimulation, such as increased serum thyroxine or triiodothyronine or decreased serum thyrotropin concentrations, as has been reported by others (10). Thyroid size was not determined, but in another study it was increased in infants born of mothers who smoked (11). Of note is their finding that cord serum thyroglobulin concentrations were increased in the infants whose fathers, but not mothers, smoked, indicating that the component(s) of tobacco smoke that stimulates thyroglobulin secretion can be transferred passively.…”