Smoking during pregnancy harms thyroid of mother, fetus

Cigarette smoking while pregnant is linked to probable detrimental changes in the mother's as well as the fetus' thyroid function, researchers reported in the Nov. 18, 2008 online edition of the Journal of Clinical Endocrinology and Metabolism.

In this cohort study, researchers followed 2,355 pregnant women. They discovered that smokers had lower levels of serum thyrotropin (TSH) and higher levels of free triiodothyronine (FT3) than nonsmokers. Influence of smoking on thyroid function was measured on two groups of women in different trimesters of pregnancy. In both groups, researchers found that smoking during pregnancy alters the mothers' thyroid hormone levels, according to Bijay Vaidya, PhD, study co-author.

Also measured were thyroid hormone levels in the umbilical cord of 618 babies born to smoking mothers. Findings showed that smoking-related changes in thyroid function also affect the fetus. As for mothers who quit smoking during pregnancy, their thyroid hormone levels were similar to levels in non-smokers.