Upper Limit for TSH of First and Second Trimester Pregnancy in Turkey

Physiological changes necessitate the use of pregnancy-specific reference ranges for TSH and FT4 to diagnose thyroid dysfunction during pregnancy. Although many centers use fixed upper limits for TSH of 2.5 or 3.0 mU/L, this may lead to overdiagnosis or even overtreatment. The new guidelines of the American Thyroid Association have considerably changed recommendations regarding thyroid function reference ranges in pregnancy accordingly. Any hospital or physician that is still using the 2.5 or 3.0 mU/l cut-off for TSH during pregnancy should evaluate their own lab-specific cut-offs. The investigator's objective is to establish a rational reference range of serum TSH for diagnosis of subclinical hypothyroidism in the first and second trimester of pregnant women in west Black Sea region in Turkey.