Thyroid dysfunction in pregnancy: definition of TSH cut-off should precede the decision of screening in low-risk pregnant women.

Objective: To evaluate the frequency of elevated TSH in pregnant women of low risk for thyroid dysfunction.

Subjects And Methods: TSH was measured in 838 pregnant women during the first trimester of gestation (from 6 to 14 weeks, median 9 weeks) and who were considered to be of low risk for thyroid dysfunction because they did not meet any of the following criteria: known or clinically suspected thyroid disease; history of head and neck radiotherapy; personal history of autoimmune diseases; family history of thyroid disease; history of abortion or prematurity.

Results: The frequency of elevated TSH was 0.25%, 1.2% and 5.5% at cut-off values of 4, 3 and 2.5?mIU/l, respectively. These rates increase to 1.43%, 2.4% and 6.2% if cases of TSH> 2 mIU/l with TPOAb are included. TSH was undetectable in 18 women (2.1%), but only six (0.71%) had elevated T4.

Conclusions: The definition of a TSH cut-off that defines subclinical hypothyroidism (SCH) should precede the decision of screening pregnant women without any risk factors for thyroid dysfunction.