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

Abstract

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.

Keywords: Autoimmune thyroid disease; Hyperthyroidism; Hypothyroidism; Iodine; Pregnancy; Thioamides; Thyroiditis.

Fig. 1

Hypothalamic-pituitary-thyroid axis and pregnancy.

Fig. 2

Treatment of maternal hypothyroidism in pregnancy TFTs, thyroid function tests. TSH, thyroid stimulating hormone. ^†These are conservative estimates based on our experience. Higher doses may be required and depending on the patients’ total body weight. We recommend regular TFTs and levothyroxine dose escalation until TSH drops within the trimester-specific reference range.

Fig. 3

Treatment of maternal hyperthyroidism in pregnancy. ^†In most patients hyperthyroidism appears outside of pregnancy and in such cases definitive treatments with thyroidectomy or radioidine ablation should be considered if pregnancy is contemplated in the near-future (see main text).