Early pregnancy testing is of paramount importance for pregnancies with mothers known to have an underactive thyroid. This is a critical period because baby’s brain is entirely dependent on maternal thyroid hormones. Using appropriate reference ranges for pregnancy and individualising treatment may lead to better thyroid control.

Reference: Ashoor G, Rotas M, Maiz N, Kametas NA, Nicolaides KH. Maternal thyroid function at 11–13 weeks of gestation in women with hypothyroidism treated by thyroxine. Fetal diagnosis and therapy. 2010;28(1):22-7.