General Considerations Relating to Thyroid Disease in Pregnancy

Thyroid hormone is essential for maintaining a pregnancy and ensuring fetal development. Thyroid disorders are common in women of childbearing age and as pregnancy has a substantial impact on the hypothalamic–pituitary–thyroid axis, abnormal thyroid function is frequently encountered in antenatal clinics. It is also well established that overt thyroid disease is associated with adverse obstetric and offspring neuro-developmental outcomes. There is now growing concern that more marginal degrees of thyroid dysfunction particularly subclinical hypothyroidism (elevated TSH and normal fT4 concentration) and isolated hypothyroxinaemia (normal TSH and low fT4) are also associated with fetal loss, prematurity and impaired offspring cognitive function. In some studies, maternal thyroid autoimmunity has also been identified as a potential risk for fetal loss even in euthyroid women. Correction of overt hypothyroidism and hyperthyroidism dramatically reduces the risk of major adverse obstetric outcomes including fetal loss and premature birth.