P&S Journal: Fall 1996, Vol.16, No.3
Premature Babies, Thyroid Hormone, and CP
Premature infants with low levels of thyroid hormones are significantly more likely to develop cerebral palsy (CP) than are infants with normal hormone levels, according to a study led by Dr. Mary Lynne Reuss, former assistant professor of clinical obstetrics and gynecology in the Sergievsky Center, and Dr. Mervyn Susser, the Gertrude Sergievsky Professor Emeritus of Epidemiology and a special lecturer in public health. The study was published in a March issue of the New England Journal of Medicine.
Experts have long believed that transient hypothyroxinemia was a common but benign occurrence among premature newborns. Recently, however, a few studies (one in the United Kingdom, one in the Netherlands) have linked hypothyroxinemia in the neonatal period to problems in motor and cognitive development. The new study is the first to show that the effects of hypothyroxinemia are independent of brain lesions in the newborn, the major known antecedent of these neurodevelopmental disorders.
In the Columbia study, researchers obtained blood thyroxine levels for 463 infants born at 33 weeks gestation or less and weighing less than four pounds. By the time they were 2 years old, babies who had severe hypothyroxinemia were 11 times more likely to have developed cerebral palsy than infants with normal thyroxine levels. When the researchers controlled for conditions such as brain damage and medical problems resulting from prematurity, the children with severe hypothyroxinemia were still at greater risk. The children also scored 7 to 18 points lower on intelligence tests.
Cerebral palsy affects approximately 500,000 people in the United States. About 15 percent of premature babies have a decrease in thyroid hormone levels after birth, though the study found that only extremely low hormone levels correlated with the development of CP.
Although the first rational response to these findings is to attempt to treat the problem with thyroid hormones, the researchers caution that controlled trials are needed to show whether such treatment is efficacious or even safe.