On the biochemical assessment of maternal thyroid function and thyroid autoantibodies in pregnancy: a review

Thyroid disease is a common endocrine disorder in pregnant women and important to recognize. The clinical management relies on biochemical assessment of thyroid function and thyroid autoantibodies from a panel of routinely available tests. A challenge regarding biochemical assessment in pregnancy relates to the physiological adaptations that influence the analyses used for diagnosis and monitoring of maternal thyroid disease. The physiological adaptations include an increased activity of the thyroid gland, an increase in the levels of binding proteins, and a suppression of the immune system which implies that biochemical test results should be interpreted in the context of pregnancy. This narrative review will discuss the biochemical assessment of thyroid function and thyroid autoantibodies in pregnancy with a focus on the biochemical methods used and the interpretation of results including strategies for establishment of reference intervals. A key implication is that biochemical results obtained in pregnancy should be considered according to the timing of the blood sampling and the biochemical method used. This is reflected by recommendations on the use of method- and trimester-specific reference intervals as part of clinical care, but similar considerations apply when thyroid function tests and thyroid autoantibodies are evaluated as part of population monitoring and used for definition of exposure in scientific outcome studies. Future research is encouraged to support the biochemical assessment and interpretation of thyroid function tests and thyroid autoantibodies in pregnancy. Future perspectives include advancements in the biochemical methods and in the methodology applied for establishment of reference intervals or clinical decision limits.