Title | Early pregnancy reference intervals of thyroid hormone concentrations in a thyroid antibody-negative pregnant population. |
Publication Type | Journal Article |
Year of Publication | 2011 |
Authors | Männistö T, Surcel H-M, Ruokonen A, Vääräsmäki M, Pouta A, Bloigu A, Järvelin M-R, Hartikainen A-L, Suvanto E |
Journal | Thyroid |
Volume | 21 |
Issue | 3 |
Pagination | 291-8 |
Date Published | 2011 Mar |
ISSN | 1557-9077 |
Keywords | Autoantibodies, Cohort Studies, Female, Gestational Age, Humans, Iodide Peroxidase, Pregnancy, Prospective Studies, Reference Values, Thyroid Gland, Thyroid Hormones, Thyroxine, Triiodothyronine |
Abstract | BACKGROUND: Thyroid dysfunction and antibodies are increasingly recognized as risk factors during pregnancy. Thyroid function changes during pregnancy and there is a need for gestational age-specific reference intervals for thyroid hormones. The aim of this study was to calculate gestational age-specific thyrotropin (TSH), free thyroxine (fT4), and free triiodothyronine (fT3) reference intervals in an iodine-sufficient thyroid antibody-negative population. METHODS: The study population consisted of a large, prospective population-based cohort, the Northern Finland Birth Cohort 1986 (singleton births, n = 9362), with extensive data throughout gestation. The subjects underwent serum sampling in early pregnancy. Samples were assayed for TSH, fT4, fT3, thyroid-peroxidase, and thyroglobulin antibodies (n = 5805). All mothers with thyroid antibodies or previous thyroid diseases were excluded when calculating gestational age-specific percentile categories for TSH, fT4, and fT3. Also, associations between body mass index (BMI) and thyroid hormones were established. RESULTS: The upper reference limit for TSH was 2.5 multiples of median (2.7-3.5 mU/L, depending on gestational week). The lower reference limit was as low as 0.07 mU/L. Reference intervals for fT4 rose during early pregnancy and decreased thereafter, ranging between 11-22 pmol/L. Reference intervals for fT3 were uniform throughout gestation, ranging between 3.4 and 7.0 pmol/L. BMI was associated positively with early pregnancy TSH and fT3 concentrations and negatively with fT4 concentrations. CONCLUSIONS: These gestational age-specific reference intervals for thyroid hormones provide a framework for clinical decision making. Overweight and obesity are increasing problems among fertile women and they are associated with possibility of thyroid dysfunction during pregnancy. |
DOI | 10.1089/thy.2010.0337 |
Alternate Journal | Thyroid |
PubMed ID | 21254924 |