A case of fetal hyperthyroidism treated with maternal administration of methimazole

Fetal Hyperthyroidism with Maternal Hypothyroidism: Two Cases of Intrauterine Therapy

Fetal hyperthyroidism can occur secondary to maternal autoimmune hyperthyroidism. The thyroid-stimulating hormone receptor antibody (TRAb) transferred from the mother to the fetus stimulates the fetal thyroid and causes fetal thyrotoxicosis. Fetuses with this condition are difficult to detect, especially after maternal Graves disease therapy. Here, we present two cases of fetal hyperthyroidism with maternal hypothyroidism and review the assessment and intrauterine therapy for fetal hyperthyroidism. Both women were referred at 22+ and 23+ weeks of gestation with abnormal ultrasound findings, including fetal heart enlargement, pericardial effusion, and fetal tachycardia. Both women had a history of Graves disease while in a state of hypothyroidism with a high titer of TRAb. A sonographic examination showed a diffusely enlarged fetal thyroid with abundant blood flow. Invasive prenatal testing revealed no significant chromosomal aberration. Low fetal serum TSH and high TRAb levels were detected in the cord blood. Fetal hyperthyroidism was considered, and maternal oral methimazole (MMI) was administered as intrauterine therapy, with the slowing of fetal tachycardia, a reduction in fetal heart enlargement, and thyroid hyperemia. During therapy, maternal thyroid function was monitored, and the dosage of maternal levothyroxine was adjusted accordingly. Both women delivered spontaneously at 36+ weeks of gestation, and neonatal hyperthyroidism was confirmed in both newborns. After methimazole and propranolol drug treatment with levothyroxine for 8 and 12 months, both babies became euthyroid with normal growth and development.

Recommendations of the AGG (Working Group for Obstetrics, Department of Maternal Diseases) on How to Treat Thyroid Function Disorders in Pregnancy

Objective These recommendations from the AGG (Committee for Obstetrics, Department of Maternal Diseases) on how to treat thyroid function disorder during pregnancy aim to improve the diagnosis and management of thyroid anomalies during pregnancy.

Methods Based on the current literature, the task force members have developed the following recommendations and statements. These recommendations were adopted after a consensus by the members of the working group.

Recommendations The following manuscript gives an insight into physiological and pathophysiological thyroid changes during pregnancy, recommendations for clinical and subclinical hypo- and hyperthyroidism, as well as fetal and neonatal diagnostic and management strategies.

Diagnosis and Management of Fetal and Neonatal Thyrotoxicosis

Background and Objectives: Clinical fetal thyrotoxicosis is a rare disorder occurring in 1-5% of pregnancies with Graves' disease. Although transplacental passage of maternal TSH receptor stimulating autoantibodies (TRAb) to the fetus occurs early in gestation, their concentration in the fetus is reduced until the late second trimester, and reaches maternal levels in the last period of pregnancy. The mortality of fetal thyrotoxicosis is 12-20%, mainly due to heart failure. Case report: We present a case of fetal and neonatal thyrotoxicosis with favorable evolution under proper treatment in a 37-year-old woman. From her surgical history, we noted a thyroidectomy performed 12 years ago for Graves' disease with orbitopathy and ophthalmopathy; the patient was hormonally balanced under substitution treatment for post-surgical hypothyroidism and hypoparathyroidism. From her obstetrical history, we remarked a untreated pregnancy complicated with fetal anasarca, premature birth, and neonatal death. The current pregnancy began with maternal euthyroid status and persistently increased TRAb, the value of which reached 101 IU/L at 20 weeks gestational age and decreased rapidly within 1 month to 7.5 IU/L, probably due to the placental passage, and occurred simultaneously with the development of fetal tachycardia, without any other fetal thyrotoxicosis signs. In order to treat fetal thyrotoxicosis, the patient was administered methimazole, in addition to her routine substitution of 137.5 ug L-Thyroxine daily, with good control of thyroid function in both mother and fetus. Conclusions: Monitoring for fetal thyrotoxicosis signs and maternal TRAb concentration may successfully guide the course of a pregnancy associated with Graves' disease. An experienced team should be involved in the management.

MATERNAL GRAVES DISEASE AND ABNORMAL CYP2D6 GENOTYPE WITH FETAL HYPERTHYROIDISM

Objective

Fetal hyperthyroidism is a rare yet potentially fatal complication of past or present maternal Graves disease (GD). Our objective was to present a unique case of fetal hyperthyroidism in a mother with a prior history of GD and a cytochrome P450 2D6 (CYP2D6) polymorphism.

Methods

The clinical course in addition to serial laboratory and imaging results are presented. These include thyroid-stimulating hormone, free thyroxine, and thyrotropin receptor antibody levels, as well as fetal ultrasound, doppler fetal heart rate, and cordocentesis testing.

Results

A 27-year-old with a history of GD previously treated with radioiodine and a known cytochrome P450 polymorphism was referred to an endocrinology clinic at 17 weeks gestation for evaluation and management of fetal thyrotoxicosis. Despite close follow-up with a multidisciplinary care team and an aggressive "block and replace" treatment approach, progressive disease resulted in intrauterine fetal demise at 28 weeks gestation.

Conclusion

To our knowledge, this is the first published case report of fetal hyperthyroidism accompanied by a maternal CYP2D6 polymorphism. We hypothesize that the maternal CYP2D6 poor metabolizer phenotype prevents formation of antithyroid drug (ATD) metabolites and thus decreases the efficacy of ATD treatment. We suggest this as an area of future research.