Association of first-trimester thyroid function test values with thyroperoxidase antibody status, smoking, and multivitamin use

Endocr Pract. 2008 Jan-Feb;14(1):33-9. doi: 10.4158/EP.14.1.33.


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.

Conclusion: 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.

Publication types

  • Multicenter Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Autoantibodies / blood*
  • Autoantigens / immunology*
  • Dietary Supplements / statistics & numerical data*
  • Female
  • Humans
  • Iodide Peroxidase / immunology*
  • Iron-Binding Proteins / immunology*
  • Pregnancy
  • Pregnancy Trimester, First / blood*
  • Pregnancy Trimester, First / ethnology
  • Pregnancy Trimester, First / immunology
  • Pregnancy Trimester, First / metabolism
  • Prenatal Care
  • Smoking* / physiopathology
  • Thyroid Function Tests*
  • Thyroid Hormones / blood
  • Thyrotropin / blood
  • Vitamins / pharmacology


  • Autoantibodies
  • Autoantigens
  • Iron-Binding Proteins
  • Thyroid Hormones
  • Vitamins
  • Thyrotropin
  • TPO protein, human
  • Iodide Peroxidase