Hypothyroidism in pregnant women can affect baby's IQ

Women should be screened for thyroid disease during the first trimester, says the author of a new study.

Published August 19, 1999 4:00PM (EDT)

An embryo during the first trimester, when its fingers are separating and taste buds forming, is solely dependent on its mother for a lot of things -- among them, the production of thyroid hormones. But when the mother has a problem making enough of them, not only can the mother's health be affected, but the baby's intelligence as well, according to a new study.

In this week's New England Journal of Medicine, Dr. James Haddow claims that pregnant women who go untreated for hypothyroidism have children with lower IQs. "I don't know anything else where you can find something, treat it and expect that the development of the child's brain would benefit," says Haddow, the director of the Foundation for Blood Research in Scarborough, Maine.

Antibodies that compromise the mother's thyroid function can cross the placenta and affect the baby's own ability to produce thyroid hormones, which only starts in the second trimester. A malfunctioning thyroid can, in severe cases, lead to mental retardation. The importance of this gland's working properly should signal to the medical community, he says, the need to screen for hypothyroidism as early as possible during pregnancy. The study also notes another benefit:
increased chances for the mother to be healthy throughout and after the pregnancy.

Located in the front of the neck, the thyroid gland creates hormones that are responsible for energy production. When the body isn't making enough of these hormones, hypothyroidism occurs; conversely, when it's producing too much, hyperthyroidism results.

Haddow and his team of researchers found that women with hypothyroidism
had children who scored four points lower in IQ tests than the children of women who didn't have the disease. In addition, they found that treatment can make a difference.
Those born to women who were not treated -- by taking supplemental thyroid hormones -- scored seven points lower than kids of healthy mothers. The kids were between the ages of 7
and 9 when tested.

While it's standard practice to test for anemia, rubella immunity, Hepatitis B and blood type during the first trimester, doctors do not routinely screen for hypothyroidism; mostly, obstetricians test when there's family history or if a woman is showing symptoms.

Although hypothyroidism occurs in about 3 percent of women of childbearing age, it often goes undiagnosed because it's difficult to detect. Hypothyroidism easily masks itself because its symptoms -- including fatigue, constipation and weight gain -- can be attributed to so many other conditions. Since a woman's body is changing so much during pregnancy, it's even harder to pinpoint the cause of symptoms. Haddow suggests that women be given a blood test that measures the levels of thyroid stimulating hormones (TSH), which he says is more accurate than the physical examinations.

The connection between hypothyroidism and IQ is not new. It was made 30 years ago. But Haddow thinks there haven't been mandatory screenings because, until now, no study as significant as this one had documented the need. (Although he believes, as with most scientific studies, that there should be follow-up research to confirm his findings.)

"The message is that we are not detecting thyroid disease and it is costing patients and their offspring delay in diagnosis and treatment," says Dr. Richard Dickey, president of the American Association of Clinical Endocrinologists. "This is pretty frightening because we should not be depriving children of intellectual capacity."

Dickey takes it another step and believes that testing should be done before a woman even gets pregnant, so she can have her hypothyroidism under control before the baby even starts to develop. While Haddow agrees that the earliest detection possible is the optimal, he says it would be difficult to execute: How do you find all these women right before they get pregnant, when many of them don't show up until they miss their period? (Easy, Dickey says: Test all women of childbearing years.)

But not everybody believes that this study will have wide-scale impact. And not all obstetricians are convinced of its importance -- at least when it comes to a few IQ points.

"Frankly, I don't think that four points of an IQ [score] is that significant and they think that's the important thing," says Dr. Carol Archie, associate professor of obstetrics and gynecology at UCLA School of Medicine. "What could be important is the health of women and the prevalence of thyroid disease. My inclination would be to say, not based on the outcome for the babies, but based on the outcome for the mothers, this might be something we should screen for."

By Dawn MacKeen

Dawn MacKeen is a former senior writer for Salon, and author of a forthcoming book about her grandfather’s survival of the Armenian Genocide, "The Hundred-Year Walk: An Armenian Odyssey" (Houghton Mifflin Harcourt, January 2016).

MORE FROM Dawn MacKeen

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