Jan. 19 (iVillage Total Health) -- If you're pregnant and have certain health issues, you may want to get a thyroid test to lower the chances of miscarriage and premature birth.

That was the recommendation from a leading expert on thyroid disease and pregnancy.

The thyroid gland in the neck influences many body functions, including growth and development, puberty, organ function, body temperatures, fertility and pregnancy. The two most common thyroid disorders are hypothyroidism (too little thyroid hormone) and hyperthyroidism (too much thyroid hormone). Together, these conditions and other thyroid disorders affect an estimated 20 million Americans, according to the American Association of Clinical Endocrinologists (AACE). Some thyroid disorders are autoimmune, which means the body's immune system produces antibodies that attack the gland.

A healthy thyroid in a mother is crucial during the first three months of pregnancy. Lack of thyroid hormone affects the normal prenatal development of a baby's brain and also affects all the associated brain functions. During pregnancy, nearly one out of every 50 women is diagnosed with hypothyroidism, and 6 percent of miscarriages are associated with thyroid deficiency. Recent studies have linked thyroid disease with premature birth and cognitive impairment in newborns.

Alex Stagnaro-Green, M.D., of the New Jersey Medical School at the University of Medicine and Dentistry of New Jersey (UMDNJ) has studied the link between thyroid dysfunction and miscarriages and premature births. He said universal thyroid screening of pregnant women may eventually become part of standard prenatal testing. His message was timed to January's observance of Thyroid Awareness Month.

Women who may be at greater risk of pregnancy complications from thyroid disorders include those with histories of miscarriage and premature birth, women with type 1 diabetes or other autoimmune disorders and anyone with family histories of those disorders. Current guidelines recommend testing only these high-risk women. Stagnaro-Green indicated that those high-risk women should be routinely screened for thyroid antibodies in their blood, which may indicate hyperthyroidism. "Just by having antibodies, their risk of miscarriage doubles," Stagnaro-Green said in a press release.

Stagnaro-Green also contends that many women may have thyroid problems but exhibit no symptoms and have normal thyroid functioning. An obstetrician may not order thyroid testing for these women even though they may be at greater risk of miscarriage and preterm births.

A separate study in the United Kingdom found that limiting thyroid testing to only high-risk women could miss about one-third of women with hypothyroidism. The researchers studied 1,560 pregnant women and conducted thyroid tests early in their pregnancies (at about 9 weeks of gestation).

The study tested levels of thyroid stimulating hormone (TSH), which would be elevated in people experiencing hypothyroidism. Only 26.5 percent of the women were considered high-risk, with either personal or family histories of thyroid disorders. However, 30 percent of the women with elevated TSH levels came from the low-risk group.

The study on TSH testing was published in the January issue of the Journal of Clinical Endocrinology & Metabolism.

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