(RxWiki News) More pregnant women may have low thyroid levels than doctors currently realize - over five times more than the currently accepted rate of two to three percent.
Having an underactive thyroid gland, known as hypothyroidism, has been associated in pregnant women with high blood pressure, gestational diabetes, miscarriage, low birth weight and potentially abnormal development in the baby's brain, but women typically aren't screened for it during prenatal care.
"Ask your OB/GYN to test for gestational hypothyroidism."
Lead author Amy Blatt and two colleagues working at Quest Diagnostics, a company which performs laboratory tests, analyzed the records of 502,036 pregnant women aged 18 to 40 whose blood was tested between June 2005 and March 2008.
They found only a quarter of those women were tested for hypothyroidism, and 15.5 percent of those women tested positive for the condition. Women over 35 and obese women were more likely to be screened and more likely to have low thyroid levels.
The authors state that their findings mean the current rate of testing for gestational hypothyroidism may be too low, potentially leaving many women undiagnosed and therefore untreated for the condition.
Although medical guidelines suggest that hypothyroidism screening be standard practice for older women's prenatal care, only a third of women over 30 were tested. Women aged 35 to 40 were 1.8 times more likely to develop the condition than women aged 18 to 24.
The researchers also found differences in the prevalence of the condition in different ethnic groups: 19.3 percent of Asian women tested positive, compared to 16.4 percent for Caucasian, 15.2 percent for Hispanic and 6.7 percent for African-American women.
Using the numbers from their study, the researchers estimate that an additional 483,000 could have had gestational hypothyroidism in 2006 and not known it. They based this estimate on the 4 million births that year and that 77 percent were not screened for the condition.
Among the women who had gestational hypothyroidism, one fifth returned for postpartum testing, and 11.5 percent of these women were diagnosed with postpartum hypothyroidism. Hispanic women had the highest rate, 16 percent, the Caucasian women, at 10 percent, had the lowest rate.
The study was published online in the Journal of Clinical Endocrinology and Metabolism and will appear in the journal's March issue. All three authors are employed at Quest Diagnostics and two have equity interest in the company.