Pregnant Women Should Be Tested for Thyroid Disorder To Prevent Mental Deficiencies in Unborn Children
Bethesda, MD, August, 18, 1999 –The Endocrine Society today called for development of cost-effective thyroid function screening for all pregnant women based on results of a study reported in the New England Journal ofMedicine showing mental defects in children whose mothers had untreated hypothyroidism during their pregnancies.
The study, conducted by Dr. James Haddow of the Foundation for Blood Research, is published in the August 19, issue of the Journal. It indicates that untreated mild thyroid failure in a mother may adversely affect thefetus’ brain development, resulting in a child with reduced IQ scores and other measurements of intelligence,aptitude and visual motor skills.
“The report suggests that testing for thyroid stimulating hormone (TSH) should be carried out before or early in pregnancy to allow adequate treatment of the mother and the fetus,” said J. Larry Jameson, M.D., Ph.D.,President of The Endocrine Society, which issued a position statement with recommendations today following review of the study.
“The signs and symptoms of hypothyroidism are nonspecific and can be masked by pregnancy; blood tests are the best way to make such a diagnosis. It now appears that maternal thyroid hormone deficiency can be added to the list of correctable maternal conditions that can have an important impact on the fetus.”
Jameson noted that the new study’s findings are consistent with previous, less extensive research. They indicate that children born without hypothyroidism to mothers who had -undetected thyroid deficiencies may develop decreased mental capacities. In IS tests administered to 7- to 9-year-old children in this category, offspring of the hypothyroid mothers performed less well on all tests.
Jameson said further research is required to determine when screening should take place, the method of testing, and diagnostic criteria for maternal hypothyroidism, treatment guidelines and costs.
“For now, women with a personal or family history of thyroid disease, or with symptoms, should have their TSH levels tested when planning pregnancy or as soon as possible after conception,” he added.
ENDOCRINE SOCIETY POSITION STATEMENT
Maternal Thyroid Hormone Deficiency During Pregnancy:
Implications for Cognitive Development in the Child
It has been controversial whether low maternal thyroid hormone levels affect the developing fetus during pregnancy. A study published on August 19, 1999 in the New England Journal of Medicine, by James E. Haddow, MD and colleagues, reports that maternal thyroid deficiency causes developmental problems for the child. The Endocrine Society believes that this study has important implications for the management of thyroid disease before and during pregnancy.
Dr. Haddow’s research team retrospectively tested serum samples for evidence of hypothyroidism in a group of 2S,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 hypothyroid during pregnancy performed less well on all tests. Their mean 10 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 thyroid hormone deficiency during pregnancy 9 adversely affects brain development.
Hypothyroidism is relatively common, occurring in about I in 100 women during the child-bearing years. It becomes more common with age, a feature which is notable as a greater number of women are deferring pregnancy until they are older. The developing fetus is unable to make its own thyroid hormone during the early stages of pregnancy. Therefore, thyroid hormone must be transferred from mother to fetus across the placenta until the fetus’ own thyroid gland starts to function during the second trimester. The consequences of maternal thyroid hormone deprivation during pregnancy appear to be substantial and irreversible.
Ideally, hypothyroidism would be detected before ., or early in pregnancy, to allow adequate treatment of the mother and the fetus. Because the signs and symptoms of hypothyroidism (e.g., fatigue, dry skin, coarsening and loss of hair, weight gain, constipation, abnormal menses) are nonspecific, and can be masked by pregnancy, blood tests are the most efficacious means to make this diagnosis. It now appears that maternal thyroid hormone deficiency can be added to the list of correctable maternal conditions such as folate deficiency, blood group incompatibility, and gestational diabetes that have important impact on the health of the developing fetus.
The Endocrine Society recommends:
- 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 hypothyroidism, treatment guidelines, and the cost of screening.
- For now, women with a personal or family history of thyroid disease, or symptoms suggestive of hypothyroidism, should be screened using TSH levels when they are planning pregnancy, or as soon as possible after conception.
- 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 percent 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.
Patients with hormone-related disorders such as hypothyroidism are commonly referred to endocrinologists, who have the specialized training and experience necessary for effective evaluation and treatment.