Autoimmune hypothyroid disease can cause problems during pregnancy.An endocrinologist's practical approach to hypothyroidism in pregnancyAll aspects of thyroid physiology change during pregnancy which makes interpretation of thyroid function more difficult. The best way to monitor hypothyrodiism in pregnancy is the Free Thyroxine Index (FTI) which is a ratio of the total T4 and the T3 resin uptake. The FTI remains constant regardless if a patient is pregnant or not. This avoids the mis-diagnosis of 'hypothyroxinemia' based on direct Free T4 measurements. Previous recommendations had suggested the use of the direct Free T4 (FT4) assay, but this method is flawed if non pregnant reference ranges are used since the levels of FT4 decrease below the normal range in the second and third trimesters. Most national labs do have have pregnancy ranges for the direct Free T4. Free T4 by equilibrium dialysis is accurate but very expensive.Details of normal thyroid hormone physiology changes during pregnancyThere are a number of changes that occur with thyroid physiology in pregnancy that are related to the hormonal changes that occur in pregnancy. At the end of pregnancy thyroid physiology reverts back to normal thyroid physiology. There is a predictable sequence of events that occurs during different stages of pregnancy. Here are the important points.
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