Preeclampsia May Lead to Reduced Thyroid Function

Women who experience preeclampsia, a serious complication of pregnancy, may have an increased risk for reduced thyroid functioning later in life, according to a new report.

Preeclampsia is a life-threatening complication that affects 3-5% of pregnancies. It results in high blood pressure and protein in the urine. Though it begins with mild symptoms, it can progress to severe preeclampsia and eclampsia—dangerously high blood pressure and convulsions that can lead to disability or death.

The causes of preeclampsia aren’t known. In earlier work, a team led by Dr. Richard J. Levine of NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) found that high levels of 2 molecules in the blood may cause symptoms of preeclampsia. One of those molecules, soluble fms-like tyrosine kinase 1 (sFlt-1), acts by blocking a protein called vascular endothelial growth factor (VEGF).

Other studies have found that some cancer patients receiving treatments that block VEGF develop hypothyroidism, a condition in which the thyroid gland fails to produce enough hormones. The thyroid gland, located in the front of the throat, makes hormones that help regulate heart rate, blood pressure, body temperature and the conversion of food into energy. Reduced thyroid functioning, or hypothyroidism, results in overall weakness and fatigue, and increases the risk for cardiovascular disease.

Levine and his colleagues set out to see whether women with preeclampsia had problems with thyroid functioning as well. Funding for their work was provided in part by NICHD and NIH’s National Heart, Lung and Blood Institute (NHLBI).

The researchers first tested blood samples collected in an earlier NIH-led study on preeclampsia for levels of thyroid stimulating hormone (TSH), which stimulates the thyroid gland. Elevated TSH may signal a malfunction of the thyroid. The scientists also drew on findings from a study in Norway, in which researchers had collected data from over 7,000 women who gave birth to a first child in 1967 or later. The women’s blood samples had been tested for thyroid function in the mid-1990s.

The researchers found a link between preeclampsia and reduced thyroid functioning, as reported in the November 2009 edition of BMJ. In the first study, women who went on to develop preeclampsia had much higher levels of TSH toward the end of their pregnancies than women who never developed preeclampsia. The rise in TSH was strongly associated with levels of sFlt-1, one of the proteins linked to symptoms of preeclampsia.

In the Norway study, women who had preeclampsia in their first pregnancy were 1.7 times as likely to have high TSH an average of 20 years later as women who hadn’t had preeclampsia. Women with preeclampsia in both their first and second pregnancies were nearly 6 times as likely to have high TSH levels.

“This suggests that a history of preeclampsia may predispose women to the later development of reduced thyroid function,” Levine says. Doctors treating women with a history of preeclampsia should be aware of a higher potential risk for reduced thyroid functioning.

“Reduced thyroid functioning is easy to diagnose when suspected, and inexpensive to treat,” says Dr. Susan B. Shurin, acting director of NICHD. “Replacement therapy substantially improves quality of life of affected persons.”