From the Guidelines
The most common fetal complication of maternal uncontrolled Graves' disease is fetal thyrotoxicosis, which can lead to severe consequences such as fetal tachycardia, intrauterine growth restriction, and heart failure. This condition occurs when maternal thyroid-stimulating immunoglobulins (TSIs) cross the placenta and stimulate the fetal thyroid gland, causing excessive production of thyroid hormones in the fetus 1. Fetal thyrotoxicosis typically develops in pregnancies complicated by Graves' disease, particularly when the mother has high levels of TSIs or is inadequately treated.
According to the American College of Obstetricians and Gynecologists (ACOG) Practice Bulletin on Thyroid Disease in Pregnancy, Graves' disease is responsible for 95 percent of hyperthyroidism cases in pregnancy, and untreated hyperthyroidism can lead to severe preeclampsia, preterm delivery, heart failure, and low birth weight in neonates 1. The bulletin also highlights the importance of monitoring women with Graves' disease for normal heart rate and appropriate growth, and considering the risk of neonatal thyroid dysfunction 1.
Key points to consider in managing maternal uncontrolled Graves' disease include:
- Optimizing maternal thyroid function with antithyroid medications, aiming for maternal free T4 in the high-normal range
- Regular fetal surveillance with ultrasound to monitor fetal heart rate, growth, and thyroid size
- Considering the risk of neonatal thyroid dysfunction and the need for consultation with a specialist if fetal thyrotoxicosis is diagnosed
- Avoiding treatment with iodine 131 (I-131) in pregnant women, as it is contraindicated and can lead to congenital hypothyroidism 1.
Overall, maintaining maternal euthyroidism is crucial to preventing fetal thyrotoxicosis and ensuring the best possible outcomes for both mother and fetus.
From the FDA Drug Label
In pregnant women with untreated or inadequately treated Graves’ disease, there is an increased risk of adverse events of ... fetal or neonatal hyperthyroidism The most common fetal complication of maternal uncontrolled Graves' disease is fetal or neonatal hyperthyroidism 2.
From the Research
Fetal Complications of Maternal Uncontrolled Graves' Disease
The most common fetal complications of maternal uncontrolled Graves' disease include:
- Fetal hyperthyroidism, which can lead to tachycardia, goiter, growth restriction, advanced bone maturation, cardiomegaly, and fetal death 3, 4, 5
- Fetal tachycardia, which can be a sign of fetal hyperthyroidism 6
- Right-ventricular hypertrophy with pericardial effusion, which can be related to untreated maternal Graves' disease 6
- Intrauterine growth restriction, which can be a result of fetal hyperthyroidism or hypothyroidism 4, 7
- Preterm birth, which can be a complication of fetal hyperthyroidism or hypothyroidism 4, 7
Fetal Hyperthyroidism
Fetal hyperthyroidism can occur when maternal thyroid-stimulating hormone receptor antibody (TRAb) levels are high, causing the fetus to produce excess thyroid hormones 3, 4. This can lead to a range of complications, including:
- Tachycardia
- Goiter
- Growth restriction
- Advanced bone maturation
- Cardiomegaly
- Fetal death
Diagnosis and Treatment
Diagnosis of fetal hyperthyroidism can be made through umbilical blood sampling and measurement of thyroid function tests 7. Treatment typically involves administering antithyroid drugs to the mother, which can help reduce fetal thyroid hormone levels 3, 4, 7. In some cases, thyroxine may be injected into the amniotic sac to treat fetal hypothyroidism 7.