Hyperthyroidism during pregnancy--the role of measuring maternal TSH receptor antibodies and foetal ultrasound monitoring.

INTRODUCTION: To evaluate the usefulness of measuring maternal anti-TSH receptor antibodies (TRAbs) and foetal ultrasound (US) monitoring in cases of current or past maternal hyperthyroidism.

MATERIAL AND METHODS: 77 pregnant women suffering from hyperthyroidism or with a history of Graves' hyperthyroidism were observed prospectively. Maternal serum TSH, fT4, fT3, TRAbs, and foetal US were performed at baseline and repeated every 2-4 weeks when needed. Neonatal thyroid status was assessed based on serum TSH, fT4 and fT3 obtained in the first days of life.

RESULTS: 35 women were diagnosed with gestational hyperthyroidism and 42 with Graves' disease; among them 26 had current and 16 past hyperthyroidism. Foetal and neonatal thyroid dysfunction occurred only in cases of maternal Graves' disease: nine (21%) and three (7%), respectively. Active maternal Graves' hyperthyroidism and TRAbs elevated at least five times above the upper normal limit predisposed to foetal hyperthyroidism. Maternal anti-thyroid drug therapy (ATD) and low TRAbs and fT4 were the risk factors of foetal hypothyroidism. Abnormal foetal thyroid sonogram was the only sign of foetal thyroid dysfunction. Four patients (9.5%) had high TRAbs in the 3rd trimester (10.8-29.9 IU/mL), but neither foetal nor neonatal thyroid dysfunctions were noted.

CONCLUSIONS: In the cases of maternal Graves' disease, foetal thyroid dysfunction occurs more often than commonly assumed. Foetal thyroid US is a valuable tool in early diagnosis and monitoring of the foetal thyroid status in pregnancy complicated by maternal Graves' disease. The evaluation of biological activity of maternal TRAbs may be helpful in prenatal diagnosis in some cases.