64 Journal of Prenatal Medicine 2012; 6 (4): 64-71 Review article Pietro Cignini 1 Ester Valentina Cafà 2 Claudio Giorlandino 1 Stella Capriglione 2 Anna Spata 3 Nella Dugo 2 1 Department of Prenatal Diagnosis, Artemisia Fetal-Ma- ternal Medical Center, Rome, Italy 2 Department of Obstetrics and Gynaecology, University of Rome “Campus Bio-Medico”, Rome, Italy 3 Department of Obstetrics and Gynaecology, University of Palermo, Italy Corresponding author: Nella Dugo Department of Obstetrics and Gynaecology, University of Rome “Campus Bio-Medico”, Rome, Italy Via Alvaro del Portillo 200 00128 Rome, Italy E-mail: nella@dugo.it Summary Thyroid diseases are common during pregnancy and an adequate treatment is important to prevent ad- verse maternal and fetal outcomes. Subclinical disea- ses are very frequent but not easily recognized wi- thout specific screening programs. In this article we try to summarize the knowledge on the physiologic change of the thyroid and pathological function dur- ing pregnancy; we also try to describe the best way of diagnosis and treatment of thyroid dysfunction. Key words: thyroid, pregnancy, hypothyroidism, hyperthy- roidism, anti-thyroid drugs. Introduction Thyroid disorders are common in pregnancy and related to maternal and fetal complications. Hyperthyroidism occurs in 0.1-0.4% of pregnant women. Whereas about 2-3% of pregnant women are hypothyroid, of whom 0.3-0.5% have overt hypothyroidism and 2-2.5% present subclinical hypothyroidism (1). At least 5-10% of women are positive for thyroid antibo- dies and have an increased risk of developing a certain degree of thyroid insufficiency during pregnancy (2). Thyroid function is influenzed by pregnancy and its dysfunction is associated with maternal and fetal morbi- dity. Moreover the role of subclinical hypothyroidism in the developement of fetal and maternal complications is not univocal (3). Indeed subclinical hyperthyroidism is not associated with adverse outcomes. Thyroid autoimmunity appears to be associated with an increased risk of miscar- riage and preterm delivery (4). In this article we aimed to review the possible adverse ma- ternal and fetal outcomes of thyroid during pregnancy and the proper management of these conditions to avoid such complications. Methods and materials We searched on PubMed using a combination of MeSH and text words to generate two subsets of quotes com- bined with “AND”, one indexing thyroid disease and the other indexing maternal and fetal outcomes. Language restrictions were applied and the authors have considered only articles in English, Italian or French. We excluded all the articles whose abstract was not available. The electronic searches were scrutinised and we ob- tained full manuscripts of all quotes considered relevant to our study. Physiology of maternal and fetal thyroid in pregnancy The thyroid undergoes physiological changes during pre- gnancy, such moderate enlargement of the gland and in- creasing of vascularization. Beta-Human chorionic gona- dotropin (∝ -HCG) causes thyroid stimulation since the first trimester, due to structural analogy with thyroid-stimu- lating hormone (TSH) (5). The thyrotropic activity of ∝ -hCG causes also a decrease in serum TSH in the first trime- ster so that pregnant women have lower serum TSH con- centrations than non-pregnant women (6). The circulating levels of thyroid-binding globulin (TBG) are also increased by estrogen stimulation. On the other hand the increased renal clearance both fetal intake and placenta metabolism induce a relative decline in the avai- lability of iodide (7). The circulating level of TBG increases, thanks to increa- sed hepatic synthesis and estrogen mediated prolonga- tion of TBG half-life from 15 minutes to 3 days, a few weeks after conception and reaches a plateau during mid-gestation (8). Total concentrations of thyroxine (T4) and of triiodothyro- nine (T3) increase in early pregnancy and achieve a pla- teau early in the second trimester, reaching a concentra- tions value of 30-100% greater than prepregnancy, primarily following the rise in TBG (9). Some authors have reported a decrease of free T4 and T3 concentrations, whereas others have reported no change or even an increase; therefore changes in free- hormone during pregnancy are controversial, though pre- gnant women in general have lower free-hormone con- centrations at term than nonpregnant women (10,11). Thyroid physiology and common diseases in pregnancy: review of literature © CIC Edizioni Internazionali