Benign thyroid disease in pregnancy: A state of the art review

•Overt hypothyroidism needs to be treated with levothyroxine.•Subclinical hypothyroidism treated with thyroxine has not been proven to improve maternal outcomes.•Overt hyperthyroidism usually needs to be treated with thioamides.•Subclinical hyperthyroidism does not require treatment.•Evidence linking TPO antibodies with miscarriages and preterm labour is unequivocal.

Thyroid dysfunction is the commonest endocrine disorder in pregnancy apart from diabetes. Thyroid hormones are essential for fetal brain development in the embryonic phase. Maternal thyroid dysfunction during pregnancy may have significant adverse maternal and fetal outcomes such as preterm delivery, preeclampsia, miscarriage and low birth weight. In this review we discuss the effect of thyroid disease on pregnancy and the current evidence on the management of different thyroid conditions in pregnancy and postpartum to improve fetal and neonatal outcomes, with special reference to existing guidelines on the topic which we dissect, critique and compare with each other.Overt hypothyroidism and hyperthyroidism should be treated appropriately in pregnancy, aiming to maintain euthyroidism. Subclinical hypothyroidism is often pragmatically treated with levothyroxine, although it has not been definitively proven whether this alters maternal or fetal outcomes. Subclinical hyperthyroidism does not usually require treatment and the possibility of non-thyroidal illness or gestational thyrotoxicosis should be considered.Autoimmune thyroid diseases tend to improve during pregnancy but commonly flare-up or emerge in the post-partum period. Accordingly, thyroid auto-antibodies tend to decrease with pregnancy progression.Postpartum thyroiditis should be managed based on the clinical symptoms rather than abnormal biochemical results.