Feature Article

Thyroid dysfunction in pregnancy: optimising obstetric outcomes

Shui-Boon Soh, Duncan J Topliss

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Abstract

Thyroid dysfunction is not uncommon in pregnancy. Women at high risk should be screened early and treated to optimise obstetric outcome. Women with pre-existing thyroid dysfunction should have their thyroid function optimised preconception.

Key Points

  • Maternal hypothyroidism should be treated with thyroxine to reduce thyroid-stimulating hormone levels to less than 2.5 mIU/L during or before the first trimester.
  • Although concern exists regarding the effect of maternal hypothyroidism on fetal IQ, this appears to be a subtle and graded phenomenon and there is no proof of benefit of thyroxine therapy. Thyroxine treatment of maternal hypothyroidism does, however, reduce other complications of pregnancy.
  • Gestational thyrotoxicosis is the most common cause of hyperthyroidism in women during the first trimester and is treated symptomatically. Graves’ disease is the most common autoimmune cause and is treated with propylthiouracil in the first trimester and with carbimazole later in the pregnancy.
  • Postpartum thyroiditis is often of autoimmune origin and can produce transient hyperthyroidism and hypothyroidism. Eventual hypothyroidism is common. It must be distinguished from postpartum Graves’ disease.
  • Thyroid nodules in pregnancy can be evaluated by ultrasonography and fine-needle biopsy. Usually definite investigation and management can be carried out postpartum.

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