Prospective evaluation of pregnant women with hypothyroidism: implications for treatment.

Pregnancy is characterized by a series of maternal hormonal and metabolic changes which can affect thyroid function and the course of thyroid dysfunction in different ways. Moreover, hypothyroidism is also associated with obstetric complications and morbidity to the fetus. The aim of the present study was to evaluate the influence of hypothyroidism during the course of pregnancy and the necessity of adjusting the dose of levothyroxine. We prospectively followed 16 patients with previous diagnosis of hypothyroidism. In ten patients (62.5%) it was necessary to raise the dose of levothyroxine, with a median increase of 20.7%. One pregnancy was complicated by premature amniorrhexis and two by pre-eclampsia. The screening for congenital hypothyroidism was negative in all newborns. We conclude that it is very important to offer screening to high-risk patients who wish to become pregnant. Dose adjustment based on serum levels of thyroid-stimulating hormone (TSH) is essential. In patients in whom TSH is not measured during the first weeks of pregnancy, a good approach could be to increase the dose of replacement therapy by 20-25% to avoid hypothyroidism.