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Thyroid hormone concentrations in blood are increased in pregnancy, partly due to the high levels of estrogen and due to the weak thyroid stimulating effects of human chorionic gonadotropin (hCG) that acts like TSH. Thyroxine (T4) levels rise from about 6–12 weeks, and peak by mid-gestation; reverse changes are seen with TSH.
Usual screening begins with assessing the thyroid stimulating hormone (TSH) level. A suppressed TSH could represent the hyperthyroid phase, but warrants further testing to investigate for possible Graves' disease. [6] A normal TSH with persistent symptoms could represent the shift between phases and requires repeat testing 4–6 weeks later; an ...
In pregnancy, subclinical hypothyroidism is defined as a TSH between 2.5 and 10 mIU/L with a normal thyroxine level, while those with TSH above 10 mIU/L are considered to be overtly hypothyroid even if the thyroxine level is normal. [44]
Many women with Hashimoto's disease develop an underactive thyroid. They may have mild or no symptoms at first, but symptoms tend to worsen over time. If a woman is pregnant and has symptoms of Hashimoto's disease, the clinician will do an exam and order one or more tests. [1] [2] [3] The thyroid is a small gland in the front of the neck.
Congenital iodine deficiency syndrome (CIDS), also called cretinism, [2] is a medical condition present at birth marked by impaired physical and mental development, due to insufficient thyroid hormone production (hypothyroidism) often caused by insufficient dietary iodine during pregnancy.
Thyroid hormones, T4 and TSH, diffuse across the placenta traveling from the mother to fetus for 10–12 weeks before the fetus’s own thyroid gland can begin synthesizing its own thyroid hormones. [2] The mother continues to supply some T4 to the fetus even after he/she is able to synthesize his/her own.
TSH levels are determined by a classic negative feedback system in which high levels of T3 and T4 suppress the production of TSH, and low levels of T3 and T4 increase the production of TSH. TSH levels are thus often used by doctors as a screening test, where the first approach is to determine whether TSH is elevated, suppressed, or normal. [25]
The target level for TSH is the subject of debate, with factors like age, sex, individual needs and special circumstances such as pregnancy being considered. [79] Recent studies suggest that adjusting therapy based on thyroid hormone levels (T 4 and/or T 3 ) may be important.