Association of first-trimester thyroid function test values with thyroperoxidase antibody status, smoking, and multivitamin use.
OBJECTIVE
To determine first-trimester thyroid function values and associations with thyroperoxidase antibody (TPO-Ab) status, smoking, emesis, and iodine-containing multivitamin use.


METHODS
We collected information by interview, questionnaire, and blood draw at the initial obstetric visit in 668 pregnant women without known thyroid disease. We compared thyroid-stimulating hormone (TSH), total thyroxine (T4), and free T4 index (FT4I) values by TPO-Ab status. Multiple regression was used to identify characteristics associated with thyroid function values.


RESULTS
The following median (range containing 95% of the data points) thyroid function test values were obtained in 585 TPO-Ab-negative women: TSH, 1.1 mIU/L (0.04-3.6); FT4I, 2.1 (1.5-2.9); and T4, 9.9 microg/dL (7.0-14.0). The following median (range containing 95% of the data points) thyroid function test values were obtained in 83 TPO-Ab-positive women: TSH, 1.8 mIU/L (0.3-6.4) (P<.001); FT4I, 2.0 (1.4-2.7) (P = .06); and T4, 9.3 microg/dL (6.8-13.0) (P = .03) (P values denote statistically significant differences between TPO-Ab-positive and negative participants). Among TPO-Ab-negative participants, TSH level was not associated with use of iodine-containing multivitamins, smoking, or race. TSH increased 0.03 mIU/L for every year of maternal age (P = .03) and decreased by 0.3 mIU/L for every increase in parity (P<.001). T4 decreased 0.04 microg/dL for every year of maternal age (P = .04). Mean FT4I was 2.05 in smokers and 2.20 in nonsmokers (P<.01). There were no relationships between T4 or FT4I and parity, race, or iodine-containing multivitamin use.


CONCLUSIONS
TPO-Ab status of pregnant women should be considered when constructing trimester-specific reference ranges because elevated serum TPO-Ab levels are associated with higher TSH and lower T4 values.
Pearce
Elizabeth N
EN
Section of Endocrinology, Diabetes, and Nutrition, Boston University Medical Center, Boston, Massachusetts, USA. elizabeth.pearce@bmc.org
Oken
Emily
E
Gillman
Matthew W
MW
Lee
Stephanie L
SL
Magnani
Barbarajean
B
Platek
Deborah
D
Braverman
Lewis E
LE
D000293:Adolescent; D000328:Adult; D001323:Autoantibodies / Q000097:blood*; D001324:Autoantigens / Q000276:immunology*; D019587:Dietary Supplements / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D007453:Iodide Peroxidase / Q000276:immunology*; D033862:Iron-Binding Proteins / Q000276:immunology*; D011247:Pregnancy; D011261:Pregnancy Trimester, First / Q000097:blood* / Q000208:ethnology / Q000276:immunology / Q000378:metabolism; D011295:Prenatal Care; D012907:Smoking / Q000503:physiopathology; D013960:Thyroid Function Tests; D013963:Thyroid Hormones / Q000097:blood; D013972:Thyrotropin / Q000097:blood; D014815:Vitamins / Q000494:pharmacology
D001323:Autoantibodies; D001324:Autoantigens; D033862:Iron-Binding Proteins; D013963:Thyroid Hormones; D014815:Vitamins; D013972:Thyrotropin; C056658:TPO protein, human; D007453:Iodide Peroxidase