Letter From The Endocrine Society

From ThyroWorld Volume 3, No 1, Spring 2000.

In late summer 1999, Dr. Larry Jameson, President of The Endocrine Society, wrote an open letter to all its members regarding important thyroid research. Dr. Robert Volpé and Dr. Larry Wood, both members of the Society, have shared this information with us for publication in ThyroWorld.

In August, 1999, the New England Journal of Medicine (volume 341, Number 8) presented the findings of a recent study which report that maternal thyroid deficiency causes developmental problems for the child. The study, by Dr. James E.Haddow, MD and colleagues has significant implications for all pregnant women who have undetected, untreated hypothyroidism.

Dr. Haddow's research team retrospectively tested serum samples for evidence of hypothyroidism in a group of 25,216 pregnant women who delivered babies between 1987 and 1990. From these samples, they identified 62 women who had been hypothyroid during pregnancy. Their children, who were ages 7 to 9 at the time of the study, were examined for possible neurological or psychological effects of hypothyroidism in utero. A battery of tests for attention, language, reading, and visual-motor performance were administered and the results were compared to those of a carefully matched control group of children whose mothers were not hypothyroid during pregnancy.

The children of the mothers who had been hypothyoid during pregnancy performed less well on all tests. Their mean IQ was reduced by 4 points compared to the control group. Larger IQ differences were seen in children born to a subset of mothers who never received any thyroid hormone treatment (mean IQ decreased by 7 points). Among this group, 19 percent of the offspring had an IQ less than 85 as opposed to 5 percent of children in the control group. This report confirms the findings of several earlier, smaller studies and it suggests that undiagnosed, untreated thyroid hormone deficiency during pregnancy adversely affects brain development.

The Endocrine Society believes this study has important implications for the management of thyroid disease before and during pregnancy. On behalf of its members, The Society will issue a policy statement, which includes the following recommendations:

• A cost-effective strategy for screening pregnant women for hypothyroidism before or early during pregnancy. This will require further research to determine when screening should take place relative to conception, the method of testing, diagnostic criteria for maternal hypotbyroidism, treatment guidelines, and the cost of screening.

• Women who are found to be hypothyroid during pregnancy should begin thyroid hormone replacement immediately to provide adequate thyroid hormone levels to the developing fetus.

• Thyroid hormone requirements increase by about 25%-50% during pregnancy. Consequently, women with known hypothyroidism should have their thyroid hormone levels monitored during pregnancy, and appropriate adjustments of thyroid hormone replacement should be made.