Scientists at Quest Diagnostics (Madison, NJ, USA) performed the first large-scale study to analyze the prevalence of hypothyroidism during pregnancy. The study was based on clinical guidelines issued by the American Thyroid Association (ATA; Falls Church, VI, USA) in 2011, and strongly suggests far more women are at risk for the disorder than suggested by prior studies.

Gestational hypothyroidism is increasingly being associated 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 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.

Pediatric endocrinologist Jon M. Nakamoto, MD, PhD, medical director for Quest Diagnostics and associate clinical professor at Rady Children's Hospital (San Diego, CA, USA) and the University of California, San Diego (CA, USA) said, "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 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), was 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.

The study also found that women aged 35 through 40 years were 1.8 times more likely to develop gestational hypothyroidism as those ages 18 through 24 years. Nearly one in five Asian women (19.3%) tested had TSH results consistent with hypothyroidism, the highest of any other ethnic group. Women weighing over 124 kg were 2.5 times as likely to develop gestational hypothyroidism as those weighing between 45 kg and 56 kg.

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.

The present study was published online in the December 2011 in the Journal of Clinical Endocrinology & Metabolism (JCEM).

Related Links:
Quest Diagnostics
American Thyroid Association
University of California, San Diego