Cerebral Palsy Associated with Low Levels of Thyroid Hormone in Premature Infants: Update, 3/1997 

In the April 1996 Research Fact Sheet we reported on articles in the March 28, 1996 issue of the New England Journal of Medicine which presented the results of a study on the potential relationship of a temporary low level of thyroid hormone in premature infants to the occurrence of severe cerebral palsy and/or mental retardation. It was reported in this study that premature infants with low levels of thyroid hormone in the first week of life developed severe cerebral palsy in greater number than expected. 

These articles raised the issues: should thyroid hormone in the first week of life be given to all premature infants who have a low level of thyroid hormone? What are the beneficial effects of providing thyroid hormone? What are the negative effects of providing thyroid hormone? 

Information about these questions is now becoming available. In the January 2, 1997 issue of the New England Journal of Medicine, a study is reported describing the results on neurological development of administering thyroid hormone to infants born at less than 30 weeks (7 months) of gestational (intrauterine) age¹. This carefully designed clinical trial was done in Holland. The conclusion is: in infants born before 30 weeks of gestation and then followed for 24 months, thyroid hormone supplementation DID NOT improve mental, motor or neurologic development. The authors point out that more information is needed about the effect of thyroid hormone supplementation in infants born less than 27 weeks of age (6 months) since the identification of a beneficial effect could have been hidden in this younger group.  

There appears to be no harmful effects of thyroid hormone supplementation, although some experts are concerned about this matter. The possible harmful effects could include the direct effect of too much thyroid on the developing brain (hyperthyroidism) or a suppression of the pituitary gland which controls the release of hormone from the thyroid gland. Neither of these negative effects were found in the recent study.  

Comment
This important and well done study helps answer the question whether all premature infants with low thyroid hormone levels should receive thyroid supplementation. The answer would appear to be: No. Would very premature infants under 27 weeks of gestational age benefit? This is still uncertain. Would premature infants benefit who have very low levels of thyroid hormone in early post natal life? We don't know. Thus, there may be special groups of premature infants that might benefit from thyroid hormone supplementation. Would there be deleterious effects of thyroid hormone supplementation in these special groups? It appears not be a problem; but it might be.
 

In December 1996, our Foundation sponsored a meeting of experts to discuss these matters. The meeting included the authors of the research papers published in March 1996 and in January 1997 (we had "preliminary information" about the January 1997 report). The need for and potential dangers of additional studies either to validate the results of the study done in Holland or to study special groups of premature infants was discussed. The scientists did not come to a final conclusion but agreed to work together to examine these questions. We will keep you informed.  

¹The Effects of Thyroxine Supplementation on Neurologic Development in Infants Born at Less than 30 Weeks Gestation; van Woscenaer W. et al.
 

© UCP Research & Educational Foundation, March 1997

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