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Pregnancy and Hypothyroidism: Autoimmune Thyroiditis and Iodine Deficiency Complicating Mother and Fetus

par Abalovich, Marcos;Glinoer, Daniel
Référence Comprehensive Handbook of Iodine, Elsevier Inc., page (1113-1122)
Publication Publié, 2009

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Résumé :

The prevalence of hypothyroidism during pregnancy is estimated to be 0.3-0.5% for overt hypothyroidism (OH) and 2-3% for subclinical hypothyroidism (SCH). The most important cause of maternal hypothyroidism is iodine deficiency, known to affect over 1.2 billion individuals in the world. If iodine nutrition status is adequate, chronic autoimmune thyroiditis is considered as the main cause of hypothyroidism. Several symptoms and signs may raise clinical suspicions, but only thyroid function tests can confirm the diagnosis. Serum TSH elevation suggests primary hypothyroidism and serum free T4 levels define whether one is dealing with SCH or OH, depending on whether free T4 is normal or below normal for gestational age. Patients should separate L-T4 ingestion and the ingestion of iron supplements vitamins containing iron, calcium supplements and soy-based food by at least 4 h. If OH is diagnosed during pregnancy, TFTs should be normalized as rapidly as possible. L-T4 dosage should be titrated rapidly to reach and thereafter maintain serum TSH concentrations lower than 2.5 mU/l (ideally lower than 2.0) or trimester-specific normal TSH ranges. TFTs should be readministered within 30-40 days. SCH has been shown to be associated with an adverse outcome for both the mother and the offspring. L-T4 treatment has been shown to improve obstetrical outcome, but has not been proved to modify long-term neurological development in the offspring. However, given that the potential benefits outweigh the potential risks, we recommend L-T4 replacement in women with SCH. After delivery, most hypothyroid women need the L-T4 dosage they received during pregnancy to be decreased to the preconception dosage. TSH level should be rechecked at 6 weeks postpartum, and it is important to continue monitoring TFTs for at least 6 months after delivery. © 2009 Elsevier Inc. All rights reserved..