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Nov. 17, 2009 -- Pregnant women who develop preeclampsia may have an increased risk for reduced thyroid function later in life, new research indicates.
About 3% to 5% of women experience preeclampsia, characterized by high blood pressure and protein in the urine that develops during the second half of pregnancy and can be dangerous for the mother and fetus.
Researchers from the National Institutes of Health (NIH) and other institutions report in the journal BMJ that women with preeclampsia may be more likely to have slightly reduced thyroid function during the last weeks of their pregnancies, but also decades later.
Richard J. Levine, MD, MPH, a senior investigator in the Eunice Kennedy Shriver National Institute of Child Health and Human Development, reports with colleagues on an analysis combining two separate studies. Each suggests a link between preeclampsia and reduced thyroid function.
The first shows that women who develop preeclampsia are more likely to have slightly reduced thyroid function during the final weeks of their pregnancies. The second study shows that women who develop preeclampsia are also more likely to have reduced thyroid function more than 20 years after giving birth.
“The findings suggest that the possible development of hypothyroidism is a consideration in patients with a history of preeclampsia,” says Susan B. Shurin, MD, acting director of the National Institute of Child Health and Human Development. “Reduced thyroid functioning is easy to diagnose when suspected and inexpensive to treat. Replacement therapy substantially improves quality of life of affected persons.”
The thyroid gland makes hormones that help regulate heart rate, blood pressure, body temperature, and the conversion of food into energy. Hypothyroidism, or reduced thyroid functioning, results in weakness, fatigue, and other symptoms.
Levine and collaborators from the Norwegian University of Science and Technology, Harvard Medical School, and Howard Hughes Medical Institute tested blood samples from an earlier study led by the NIH for levels of thyroid stimulating hormone, or TSH, which stimulates the thyroid gland to make thyroid hormones. TSH is typically elevated with hypothyroidism.
The U.S. study was based on thyroid function tests from 140 pregnant women who had developed preeclampsia and 140 pregnant women who hadn’t.
Before the onset of preeclampsia, both groups of women had similar levels of TSH and other thyroid function tests. After the onset of preeclampsia, women in the preeclampsia group had higher levels of TSH than the women without preeclampsia.
The researchers also examined data from Norway, where 7,121 women who’d given birth to a first child in 1967 or later had had their blood sampled for thyroid function in the mid-1990s.
The women who had preeclampsia in their first pregnancy were more likely to have high TSH years later than the women without history of preeclampsia, the researchers report. The scientists say the association was especially strong if preeclampsia had occurred in two pregnancies.
Women with a history of preeclampsia also have an increased risk of kidney disease, as well as high blood pressure and other cardiovascular problems.
The rise in TSH levels was strongly associated with levels of a protein called soluble fms-like tyrosine kinase 1, and the increase was greater in the women with preeclampsia. The researchers write that this suggests that the effect of preeclampsia on thyroid function may be mediated by this protein.