From the Guidelines
Fetal thyrotoxicosis is detected through a combination of maternal history, laboratory testing, and fetal monitoring, with the most important first step being identifying pregnancies at risk, particularly in mothers with current or past Graves' disease who have elevated thyroid-stimulating immunoglobulins (TSI) or thyroid-stimulating hormone receptor antibodies (TRAb) 1.
Detection and Diagnosis
The detection of fetal thyrotoxicosis involves several key steps:
- Identifying pregnancies at risk, especially those with a history of Graves' disease or elevated TSI/TRAb levels
- Laboratory assessment, including measurement of maternal TSI/TRAb levels, with values greater than 3 times the upper limit of normal indicating high risk for fetal thyrotoxicosis
- Fetal ultrasound monitoring after 20 weeks gestation to look for signs such as fetal tachycardia, intrauterine growth restriction, accelerated bone maturation, goiter, or heart failure
- Fetal heart rate monitoring, as persistent tachycardia is often the earliest sign of fetal thyrotoxicosis
Treatment and Management
If fetal thyrotoxicosis is suspected, treatment typically involves:
- Administering antithyroid medications to the mother, such as propylthiouracil (PTU) in the first trimester or methimazole in the second and third trimesters, as recommended by recent guidelines 1
- Close monitoring of both maternal and fetal thyroid status throughout pregnancy, with adjustments to medication as needed to maintain euthyroidism
- In some cases, additional administration of levothyroxine to the mother may be necessary to maintain her euthyroid state while treating the fetus
Key Considerations
- The goal of treatment is to maintain euthyroidism in both the mother and the fetus, minimizing the risk of complications such as preeclampsia, preterm delivery, and low birth weight
- Regular monitoring of fetal heart rate and ultrasound assessments are crucial for early detection and management of fetal thyrotoxicosis
- Collaboration between obstetricians, endocrinologists, and other healthcare professionals is essential for optimal management of fetal thyrotoxicosis 1
From the Research
Detection of Fetal Thyrotoxicosis
To detect fetal thyrotoxicosis, several methods can be employed, including:
- Monitoring for fetal thyrotoxicosis signs, such as fetal tachycardia, fetal goiter, and history of spontaneous abortions 2, 3
- Measuring maternal TRAb concentration, which can indicate the risk of fetal thyrotoxicosis 2, 3
- Assessing fetal heart rate and growth, although this method may be inaccurate 4
- Using ultrasound to detect fetal goiter, ascites, craniosyntosis, fetal growth retardation, maceration, and hydrops 3
Maternal Factors
Maternal factors that can contribute to fetal thyrotoxicosis include:
- A history of Graves' disease, which can increase the risk of fetal thyrotoxicosis 2, 3, 4
- The presence of active autoimmune thyroid disease or a history of treatment for it 3
- The transfer of thyroid-stimulating immunoglobulins from mother to fetus through the placenta 3, 4
Treatment and Management
Treatment and management of fetal thyrotoxicosis typically involve:
- Administering antithyroid medications, such as methimazole or carbimazole, to the mother, which can be transferred to the fetus through the placenta 2, 3
- Monitoring fetal heart rate and adjusting the dose of antithyroid medication accordingly 3
- Adding thyroxine to the mother's treatment regimen if she becomes hypothyroid due to antithyroid medication 3