Screening for overt thyroid disease in early pregnancy may be preferable to searching for small aberrations in thyroid function tests

Thyroid hormones are important regulators of foetal development, and in recent years, there has been much focus on the screening and treatment of pregnant women for even small aberrations in thyroid function tests. We searched PubMed for publications on thyroid function and pregnancy outcomes including child cognition, and included references from the retrieved articles. Both small aberrations in thyroid function tests in early pregnancy and an increase in risk of pregnancy complications may be caused by a functional change in the uteroplacental unit. Thus, the association found in several studies between small thyroid test abnormalities and pregnancy complications may be due to confounding, and thyroid hormone therapy will have no effect. On the other hand, screening of thyroid function in early pregnancy may identify 200-300 women with undiagnosed overt hypothyroidism per 100 000 pregnancies, which is at least five times more than the number of hypothyroid newborns identified by screening. A number of studies indicate that untreated overt thyroid disease in pregnancy may lead to complications. The potential benefit of screening and early therapy is supported by evidence, indicating that even severe maternal hypothyroidism does not lead to neurocognitive deficiencies in the child, if the condition is detected and treated during the first half of pregnancy. Screening and therapy for overt thyroid dysfunction in early pregnancy may be indicated, rather than focusing on identifying and treating small aberrations in thyroid function tests.