Graves Hyperthyroidism and Pregnancy: A Clinical Update

Komal Patil-Sisodia, MD; Jorge H. Mestman, MD


Endocr Pract. 2010;16(1):118-129. 

In This Article

Fetal Complications

Fetal and neonatal risks are directly correlated to maternal control of hyperthyroidism. The most common manifestations of uncontrolled or poorly treated maternal hyperthyroidism are intrauterine growth retardation, prematurity, low birth weight, and stillbirth. Consultation with a maternal fetal medicine colleague is advisable in the care of these patients.[48,49] Serial ultrasonography and fetal nonstress test for assessment of fetal well-being is recommended starting at about 32 weeks' gestation, although to our knowledge, no controlled studies have been conducted.

Fetal Hypothyroidism

In a mother on antithyroid drug therapy, the detection of fetal goiter by ultrasonography is an indication of fetal hypothyroidism and the need to reduce or stop the drug. In such cases, polyhydramnios is present. Intra-amniotic administration of levothyroxine has been used with resolution of the goiter;[50] however, discontinuation of antithyroid drug therapy appears to be equally effective.

Fetal Hyperthyroidism

Fetal hyperthyroidism may occur when a mother with previous ablation therapy for Graves hyperthyroidism has persistently high TRAb titers (TSH-binding inhibitory immunoglobulins >50) after 24 weeks' gestation. Antibodies crossing the placental barrier stimulate fetal thyroid with the development of fetal tachycardia, goiter, oligohydramnios, intrauterine growth retardation, and accelerated bone maturation—typical signs of fetal thyrotoxicosis.[49] The most common sign is fetal tachycardia, although it is not always present. Cordocentesis, an invasive technique to sample cord blood for assessment of thyroid function is associated with high morbidity and mortality, and should only be performed at experienced centers.[51] Treatment consists of administering methimazole to the mother, starting with 10 to 20 mg, adjusting the dosage every few days by assessing fetal tachycardia and goiter. The amount of methimazole must be monitored very carefully to prevent the development of fetal hypothyroidism.

Neonatal Hyperthyroidism

Neonates of hyperthyroid mothers with high TRAb titers are at risk of developing hyperthyroidism a few days after birth. It is a rare condition affecting 1% to 5% of infants of mothers with Graves hyperthyroidism. During pregnancy, the fetus is protected by the antithyroid drug given to the mother. Within 24 to 72 hours after delivery, affected neonates develop symptoms of hyperthyroidism including congestive heart failure. Therefore, alerting the neonatologist of potential neonatal risk before the baby is born is of paramount importance.[52] Neonatal hyperthyroidism is sometimes diagnosed when fetal hyperthyroidism was missed in infants of mothers treated with ablation therapy before pregnancy who have high TRAb titers. These babies are severely affected and have accelerated bone maturation and craniosynostosis and are small for gestational age.[53] The half-life of TRAb is about 2 to 8 weeks; therefore, neonatal hyperthyroidism is a transient entity.

Hypothalamic or Central Hypothyroidism

Hypothalamic or central neonatal hypothyroidism has been reported in infants of mothers with uncontrolled hyperthyroidism throughout pregnancy.[54] Loss of normal thyroid morphologic characteristics and decreased thyroid volume have also been documented in these children.[55] Levothyroxine treatment and long-term follow-up is recommended.