Monitoring critical, even during early months

The dangers of low thyroid function to pregnant women and their babies are well-established; the problem is awareness, experts say.

Women with a thyroid function decrease should take at least 30 percent more of the hormone they are taking to treat it until delivery -- starting at the earliest sign of pregnancy, according to a study first published last year in the New England Journal of Medicine .

"The biggest change based on these data is that women of childbearing age [with hypothyroidism] 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," the lead author of the study, Dr. Erik K. Alexander, told HealthDay .

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

At least 1 percent of American women have low thyroid function, said Alexander, an associate physician at Brigham and Women's Hospital in Boston . Untreated hypothyroidism in a pregnant woman can lead to a greater risk of a miscarriage, spontaneous abortion, fetal growth retardation, premature labor and delivery, congenital malformations and maybe even preeclampsia, experts say.

In most cases, hypothyroidism is caused by a condition in which a person's immune system attacks and destroys the thyroid, according to the American Thyroid Association. Hypothyroidism also can be caused by treatment of hyperthyroidism or by certain medications, and it may be present from birth.

Pregnancy also can cause the thyroid to become temporarily underactive. Gland inflammation from a viral infection can cause thyroid function to decrease. Finally, a problem with the pituitary gland can cause hypothyroidism as well.

Experts agree that a careful watch should be kept for signs of thyroid trouble during pregnancy.

"The physician should sit down and ask if there is a history of thyroid problems and should look for signs and symptoms of it," Dr. Stephen H. LaFranchi, head of pediatric endocrinology at the Oregon Health & Science University and a spokesman for the American Thyroid Association, told HealthDay .

The problem with that approach is that many of the symptoms of low thyroid function, including being tired, are common in any pregnancy, he said. But 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 their pregnancies.