SAN FRANCISCO -- Women with a history of Graves' disease should be screened for fetal hyperthyroidism at 2426 weeks' gestation, Dr. Ingrid Block advised at a meeting on antepartum and intrapartum management.
These women should have their thyroid-stimulating immunoglobulin (TSI) levels measured at the beginning of pregnancy and again at 24-26 weeks. The results may help confirm a suspicion of fetal hyperthyroidism or prompt further analysis, she said at the meeting, sponsored by the University of California, San Francisco.
In most laboratories, a normal background TSI titer will be less than 130%. A TSI of 350% with a fetal heart rate below 160 beats per minute suggests a low risk for fetal hyperthyroidism, but continued monitoring in these cases is prudent, said Dr. Block of the university.
A fetal heart rate above 160 beats per minute typically characterizes the disease.
A TSI of 350%-500% puts the fetus at moderate risk for hyperthyroidism, and a TSI of more than 500% puts the fetus at high risk.
Fetal hyperthyroidism complicates 1% of pregnancies in U.S. women with a history of Graves' disease. With active maternal disease, most fetuses will be protected by their mothers' antithyroid medication.
Physicians should be especially careful to look for fetal hyperthyroidism in women with a history of Graves' disease who are on thyroid hormone replacement therapy but have discontinued antithyroid medication. These women may still have thyroid-stimulating hormone (TSH)-receptor antibodies, which puts them at highest risk for fetal hyperthyroidism, she said.
In general, a maternal TSH-receptor antibody titer above 350% increases the likelihood that the fetus has hyperthyroidism.
Diagnosis is based on clinical symptoms and ultrasound findings. Ultrasound studies should be ordered for women with a history of Graves" disease to look for fetal, goiter or a hyperextended fetal neck that could indicate goiter.
Growth retardation, increased fetal motility, or accelerated fetal bone maturation also can be signs of fetal hyperthyroidism. If the woman had a previous pregnancy complicated by fetal hyperthyroidism, this also increases the risk for the disease in the current pregnancy.
In rare cases, obtaining a sample of fetal cord blood may be necessary to make the diagnosis, but this procedure carries a 1% risk of fetal loss.
Physicians should therefore weigh the risks and benefits carefully and consult a pediatric endocrinologist before performing this procedure, Dr. Block commented.
ARTICLES BY SHERRY BOSCHERT San Francisco Bureau
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