Association of First-Trimester Thyroid Function Test Values with Thyroperoxidase Antibody Status,Smoking, and Multivitamin Use |
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| Institution: | 1. Section of Endocrinology, Diabetes, and Nutrition, Boston, Massachusetts;2. Department of Laboratory Medicine, Boston University Medical Center, Boston, Massachusetts;3. Department of Ambulatory Care and Prevention, Harvard Medical School and Harvard Pilgrim Health Care, Boston, Massachusetts;4. Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts;5. Department of Obstetrics and Gynecology, Harvard Vanguard Medical Associates, Boston, Massachusetts.;1. Women''s Hospital, School of Medicine, Zhejiang University, Xueshi Road #2, Hangzhou 310006, China;2. Department of Laboratory Medicine, Changi General Hospital, 2 Simei Street 3, Singapore 529889, Singapore;1. UCL EGA Institute for Women''s Health, University College London, London, United Kingdom;2. Anu Research Centre, UCC Department of Obstetrics and Gynaecology, 5th Floor, Cork University Maternity Hospital, Wilton, Cork, Republic of Ireland |
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| Abstract: | ObjectiveTo determine first-trimester thyroid function values and associations with thyroperoxidase antibody (TPO-Ab) status, smoking, emesis, and iodine-containing multivitamin use.MethodsWe 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.ResultsThe 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 μg/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 μg/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 μg/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.ConclusionTPO-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. (Endocr Pract. 2008;14:33-39) |
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