Endocrine Abstracts

Hypothyroidism in pregnancy is generally considered harmful. However, the definition of hypothyroid during pregnancy remains controversial. Measurements of maternal serum TSH have traditionally been used to define hypothyroidism, with values >2.5 mIU/l generally warranting treatment. However, recent data have suggested that the ‘normal’ reference range for serum TSH in healthy pregnant women varies by region as well as by ethnicity. Importantly, changing the upper reference range for maternal serum TSH during pregnancy from 2.5 mIU/l to 4.5 mIU/l can impact treatment decisions for millions of women worldwide. This symposium will explore the most recent data pertaining to this complex topic, and also explore the subgroup of pregnant women with normal serum TSH values but low free thyroxine concentrations. What is a normal TSH concentration during pregnancy? What values of serum TSH are harmful to the pregnancy or the developing fetus?