[Management of Graves' disease and hypothyroidism in pregnancy]

In the treatment of pregnant patients with Graves' disease, propylthiouracil is preferred over methimazole in early pregnancy because of a possible teratogenicity of methimazole. Methimazole is preferable to propylthiouracil in other time of pregnancy on the basis of severe liver dysfunction occasionally caused by propylthiouracil. Fetal hypothyroidism can be avoided when maternal free T4 levels are maintained at or above the upper normal limit for non-pregnant subjects. However, maternal free T4 should be kept normal for pregnant reference range when pregnancy complications develop. Fetal hypothyroidism in this setting will not affect the infant's development as long as mothers are euthyroid and the infants recover from hypothyroid state within a short time after birth. In hypothyroid women, 1-T4 dose often needs to be increased in pregnancy. Maternal T4 deficiency in early pregnancy has been suggested to affect normal brain development in the offspring. However, it has recently been shown in iodine rich area that no adverse effect on neuropsychological development was seen irrespective of the severity of maternal T4 deficiency. Insufficient iodine intake in the mother can cause low T4 in pregnancy and also inadequate production of T4 in breast-fed infants when sufficient T4 is essential for normal brain development.