Pregnant Women Need to Monitor Their Thyroid

Those with underactive gland should boost thyroid hormone intake

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By
HealthDay Reporter

WEDNESDAY, July 14, 2004 (HealthDayNews) -- Women struggling with diminished thyroid function should increase their intake of thyroid hormones at the earliest sign of pregnancy, a new study indicates.

The dangers of hypothyroidism -- low thyroid function -- to mother and fetus are well-established, said Dr. Erik K. Alexander, lead author of the study that appears in the July 15 issue of the New England Journal of Medicine.

"The biggest change based on these data is that women [with hypothyroidism] of childbearing age need to be aware of the need for increasing their thyroid dose very early in pregnancy, even before they visit the obstetrician for the first time," said Alexander, an associate physician at Brigham and Women's Hospital in Boston.

The study also offers a recommendation for the size of the increase -- at least 30 percent more of the hormone than the woman had been taking, a dose that should be maintained until delivery.

The thyroid is a butterfly-shaped gland located at the base of the neck. It produces two hormones -- T4 (thyroxine) and T3 (triiodothyronine) -- that control metabolism.

At least 1 percent of American women have low thyroid function, Alexander said. Untreated hypothyroidism during pregnancy can lead to an increased risk of miscarriage, spontaneous abortion, fetal growth retardation, premature labor and delivery, congenital malformations and possibly preeclampsia, experts say.

Hypothyroidism is usually treated with medication that contains thyroid hormone.

The potential problems of an underactive thyroid are serious enough to have spurred debate about whether all women of childbearing age should be screened for low thyroid function, said Dr. Stephen H. LaFranchi, head of pediatric endocrinology at the Oregon Health & Science University, and a spokesman for the American Thyroid Association.

That debate has not been resolved, but experts agree that a careful watch should be kept for signs of thyroid trouble during pregnancy, he said.

"The physician should sit down and ask if there is a history of thyroid problems and should look for signs and symptoms of it," LaFranchi said. The exact dosage should be decided on a patient-by-patient basis, he said.

The drawback to that approach is that many of the symptoms of low thyroid function, such as fatigue, can occur in any pregnancy, he said. Two symptoms that point specifically to a thyroid problem are a very rapid heartbeat and weight loss, LaFranchi said.

The study led by Alexander included 19 women who had 20 pregnancies, 17 of which resulted in full-term births. To keep their thyroid levels up to normal, the dose of hormone they were taking had to be increased by an average of 47 percent in the first half of pregnancy.

Until the screening debate is resolved, Alexander said, "both endocrinologists and primary-care physicians should know that if a woman is on thyroid hormone, she needs to be aware of the first signs of pregnancy."

"It is important to undertake population studies to see if we should screen all women," LaFranchi added.

More information

For more on hypothyroidism and pregnancy, visit the New York Thyroid Center.

SOURCES: Erik K. Alexander, M.D., associate physician, Brigham and Women's Hospital, Boston; Stephen H. LaFranchi, M.D., head, pediatric endocrinology, Oregon Health & Science University, Portland; July 15, 2004, New England Journal of Medicine

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