Cigarette smoking during pregnancy is associated with alterations in maternal and fetal thyroid function.
BACKGROUND
Studies in the general population have shown lower serum TSH levels in smokers as compared with nonsmokers.


OBJECTIVE
Our aim was to examine whether smoking is associated with changes in thyroid function of pregnant women and their fetus.


METHODS
We examined the relationship between smoking and thyroid function (serum TSH, free T4, and free T3) in two independent cohorts of pregnant women without a history of thyroid disorder or an overt biochemical thyroid dysfunction: 1) first-trimester cohort (median gestation 9 wk) (n = 1428) and 2) third-trimester cohort (gestation 28 wk) (n = 927). We also analyzed the relationship between maternal smoking and thyroid hormone levels in cord serum of 618 full-term babies born to the women in the third-trimester cohort.


RESULTS
In smokers compared with nonsmokers, median serum TSH was lower (first-trimester cohort: 1.02 vs. 1.17 mIU/liter, P = 0.001; third-trimester cohort: 1.72 vs. 1.90 mIU/liter, P = 0.037), and median serum FT3 was higher (first-trimester cohort: 5.1 vs. 4.9 pmol/liter, P < 0.0001; third-trimester cohort: 4.4 vs. 4.1 pmol/liter, P < 0.0001). In both cohorts, serum FT4 in smokers and nonsmokers were similar. The prevalence of anti-thyroperoxidase antibodies was also similar in smokers and nonsmokers in both cohorts. Cord serum TSH of babies born to smokers was lower than of those born to nonsmokers (6.7 vs. 8.1 mIU/liter, P = 0.009).


CONCLUSIONS
Cigarette smoking is associated with changes in maternal thyroid function throughout the pregnancy and in fetal thyroid function as measured in cord blood samples.
Shields
Beverley
B
Department of Endocrinology, Peninsula Medical School, Royal Devon, Exeter Hospital, Exeter EX2 5DW, United Kingdom.
Hill
Anita
A
Bilous
Mary
M
Knight
Beatrice
B
Hattersley
Andrew T
AT
Bilous
Rudy W
RW
Vaidya
Bijay
B
D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D005312:Fetal Blood / Q000737:chemistry; D005333:Fetus / Q000503:physiopathology*; D006801:Humans; D008297:Male; D018811:Maternal Exposure / Q000009:adverse effects; D008431:Maternal-Fetal Exchange / Q000502:physiology; D009035:Mothers; D018812:Paternal Exposure / Q000009:adverse effects; D011247:Pregnancy; D011248:Pregnancy Complications / Q000097:blood / Q000503:physiopathology; D012907:Smoking / Q000009:adverse effects*; D013959:Thyroid Diseases / Q000196:embryology / Q000209:etiology; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000503:physiopathology*; D013963:Thyroid Hormones / Q000097:blood; D013972:Thyrotropin / Q000097:blood; D014029:Tobacco Use Disorder / Q000097:blood / Q000150:complications / Q000503:physiopathology*; D055815:Young Adult
D013963:Thyroid Hormones; D013972:Thyrotropin