Second trimester levothyroxine treatment for subclinical hypothyroidism or hypothyroxinaemia of pregnancy does not improve cognitive outcomes of children.

Overt thyroid disease, be it overt hypothyroidism or overt hyperthyroidism, is associated with a multitude of adverse outcomes during pregnancy including miscarriage, gestational hypertension, gestational diabetes, preterm delivery and decreased IQ in the offspring.1 In its most severe form, overt hypothyroidism results in cretinism. The impact of subclinical hypothyroidism (SCH) on pregnancy outcomes is complex. Observational and retrospective studies have shown a correlation with adverse maternal and fetal events.2 In 1999, Pop et al 3 and Haddow et al 4 reported a correlation between hypothyroidism and isolated hypothyroxinaemia (IH) with decreased neurocognitive function in the offspring. However, only two prospective randomised studies have evaluated the impact of levothyroxine therapy for SCH or IH on pregnancy outcomes. In an Italian study, levothyroxine therapy for SCH in thyroid antibody-positive women in the first trimester of pregnancy …