Am J Perinatol 1988; 5(2): 152-158
DOI: 10.1055/s-2007-999676
ORIGINAL ARTICLE

© 1988 by Thieme Medical Publishers, Inc.

Universal Predictive Criteria for Neonatal Overt Thyrotoxicosis Requiring Treatment

Haruo Tamaki, Nobuyuki Amino, Mieko Aozasa, Masao Mori, Yoshinori Iwatani, Junko Tachi, Osamu Nose, Osamu Tanizawa, Kiyoshi Miyai
  • Departments of Laboratory Medicine, Pediatrics, and Obstetrics and Gynecology, Osaka University Medical School, Osaka Japan
Further Information

Publication History

Publication Date:
04 March 2008 (online)

ABSTRACT

The universal predictive criteria for neonatal overt thyrotoxicosis requiring treatment were examined in 108 neonates (including a pair of twins) born to mothers with Graves' disease (36 patients under treatment with antithyroid drugs [group A] and 71 in remission [group B]). Anti-thyroid-stimulating hormone (TSH) receptor antibody activity was measured by both radioreceptor assay (TSH-binding inhibitor immunoglobulin [TBII]) and biologic stimulation assay (thyroid stimulating antibody [TSAb]). For generalization of the predictive criteria, the expression of TBII activity was standardized using standard serum made taking units of Medical Research Council long-acting thyroid stimulator, standard B as a reference, and expression of TSAb activity was standardized using bovine TSH as a standard. TBII activity was positive in 22 mothers at delivery, and TSAb activity was positive in 18. In 12 cases, both activities were positive. Both the TBII and the TSAb activity of maternal serum at delivery correlated well with that of the cord serum. Neonatal thyrotoxicosis occurred in 9 of 108 neonates (8%), of whom five (5%) had clinical overt symptoms requiring antithyroid drug treatment. In all nine cases the TBII and TSAb activities were both positive, but no neonate without TBII or TSAb activity developed thyrotoxicosis. The prediction rate (42%) of neonatal overt thyrotoxicosis was higher when both TBII and TSAb were measured than when only TBII (23%) or TSAb (28%) was measured. Clinical overt thyrotoxicosis could be predicted in five of six neonates (83%) of mothers when the cutoff levels of antibody activities were increased to a TBII activity of above 8 U/ml and TSAb activity of above 1.0 TSH μUEq. As a more useful predictive criterion, a new index was introduced, the binding-stimulation (BS) index, which means the product of the TBII and TSAb levels. Neonatal overt thyrotoxicosis could be predicted in all cases irrespective of the antithyroid drug treatment when the value of this new index was above 15. Methimazole did not always cause neonatal transient hypothyroidism even when given at a high dose or when the BS index was smaller. These data indicate that: (1) prediction of neonatal thyrotoxicosis is more accurate and general when both TBII and TSAb are measured and the expressions of their activities are standardized; (2) neonatal overt thyrotoxicosis can be predicted with certainty when the BS index is above 15, irrespective of the antithyroid drug treatment; and (3) the occurrence of neonatal transient hypothyroidism due to methimazole does not depend simply on the dose of this antithyroid drug or the BS index.

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