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16% of Pregnant Women Test Positive for Hypothyroidism

  • Published: 2012-01-04 (Revised/Updated 2013-06-16) : Author: Quest Diagnostics
  • Synopsis: As many as one in six pregnant women tested positive for gestational hypothyroidism or under-active thyroid during pregnancy.
Hypothyroidism - A condition in which the body lacks sufficient thyroid hormone. Estimates vary, but approximately 10 million Americans have this common medical condition. In fact, as many as 10% of women may have some degree of thyroid hormone deficiency.

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"Women ages 35 through 40 years were 1.8 times more likely to develop gestational hypothyroidism as those ages 18 through 24 years."

Study of half a million pregnant women in the United States finds 15.5% of those tested were positive for gestational hypothyroidism, much higher than prior estimates.

As many as one in six pregnant women tested were positive for gestational hypothyroidism, or under-active thyroid during pregnancy, under new clinical guidelines for detecting the disorder, according to a study published in The Journal of Clinical Endocrinology & Metabolism (JCEM).

The findings, based on a review of laboratory tests of 502,036 pregnant women in the United States, found that 15.5% of patients, or about one in six, were positive when tested. The study, by scientists at Quest Diagnostics (NYSE: DGX), is the first large-scale study to analyze the prevalence of hypothyroidism during pregnancy based on clinical guidelines issued by the American Thyroid Association (ATA) in 2011, and strongly suggests far more women are at risk for the disorder than suggested by prior studies.

A growing body of research associates gestational hypothyroidism with a range of medical complications for women and their babies, including miscarriage, pregnancy-induced hypertension, gestational diabetes, low-birth weight and abnormal fetal brain development which may lead to a lower IQ. The disorder can escape detection without the aid of widely available and inexpensive laboratory tests to identify heightened blood levels of thyroid stimulating hormone (TSH). The ATA's guidelines are the first from a medical association to recommend specific reference ranges for TSH blood levels based on recent data showing an association between low TSH levels, once believed to be harmless, and adverse health outcomes. The condition can be treated with FDA-approved oral therapies.

"Our findings should re-invigorate the medical community's long standing debate about the best approach to clinical assessment and management of thyroid function during pregnancy," said co-investigator and board-certified pediatric endocrinologist Jon M. Nakamoto, M.D., Ph.D., medical director for Quest Diagnostics and associate clinical professor at Rady Children's Hospital and the University of California, San Diego. "With the growing awareness of risks that even subclinical hypothyroidism can pose for the mother and fetus, it's important that practitioners recognize the true prevalence of this condition."

The study, titled "National Status of Testing for Hypothyroidism During Pregnancy and Postpartum," assessed results of 502,036 pregnant women who received lab testing through Quest Diagnostics between 2005 and 2008. Of these women, only about one in four, or 23% (117,892), were tested for TSH level. Among the pregnant women who were tested for TSH level, 18,291, or 15.5%, had heightened levels of TSH consistent with hypothyroidism as defined by the ATA guidelines. By comparison, older, but widely cited studies suggest a percentage rate of gestational hypothyroidism in the low single digits.

The investigators also estimated that as many as 483,000 pregnant women could have had undetected gestational hypothyroidism in the United States in 2006, based on that year's estimated 4 million live births and the study's findings of a 15.5% prevalence rate.

Other key findings from the present study include:

The study also found that only one in five women, or 20.7%, with gestational hypothyroidism were tested within six months after giving birth. Of these women, 11.5% tested positive for hypothyroidism. Symptoms of postpartum hypothyroidism can range from fatigue and depression to irritability and weight gain.

"Based on our study, it is likely that many women in the United States who have hypothyroidism during pregnancy also have, but are not treated, for hypothyroidism following their pregnancy," said Harvey W. Kaufman, M.D., senior medical director, Quest Diagnostics. "We hope that our study is a call to action for much needed additional research into gestational and postpartum hypothyroidism and the potential of readily available oral therapies to improve outcomes for women and their infants."

The present study is expected to appear in the March 2012 issue of JCEM and was published online in December 2011.

The study is part of Quest Diagnostics Health Trends, a series of reports provided as a public service on health conditions based on the company's uniquely large repository of laboratory testing data. Other Quest Diagnostics Health Trends reports have focused on gestational diabetes, heart disease, H1N1 flu and allergies and asthma. Visit

Quest Diagnostics' Expertise in Women's Health

Quest Diagnostics is a comprehensive provider of laboratory testing, research and consultation for women's health disorders across the continuum of a woman's life. The company's specialized services include genetic prenatal carrier tests for diseases such as spinal muscular atrophy, cystic fibrosis and Fragile X; cervical cancer and sexually transmitted disease testing; and pregnancy-related genetic counseling for clinicians and parents. The company's scientists also produce original research on women's health issues published in peer-reviewed journals and at scientific conferences.

About Quest Diagnostics: Quest Diagnostics is the world's leading provider of diagnostic testing, information and services that patients and doctors need to make better healthcare decisions. The company offers the broadest access to diagnostic testing services through its network of laboratories and patient service centers, and provides interpretive consultation through its extensive medical and scientific staff. Quest Diagnostics is a pioneer in developing innovative new diagnostic tests and advanced healthcare information technology solutions that help improve patient care.

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