Disclosures: The Calcium for Preeclampsia Prevention trial and the substudy presented here were funded by the National Institutes of Health. The substudy of the Nord-Trondelag Health Study was supported by the Norwegian University of Science and Technology and by the Central Norway Regional Health Authority. One of the investigators has financial ties to several pharmaceutical companies and has been named coinventor on several patents related to preeclampsia.
New evidence has strengthened the link between preeclampsia and reduced thyroid function during pregnancy, and has shown that the association persists for decades.
Women who have had preeclampsia should be monitored for reduced thyroid function after pregnancy, according to Dr. Richard J. Levine.
“We can't say for sure until we have some other studies out there that will link it more tightly,” Dr. Levine of the National Institute of Child Health and Human Development's division of epidemiology, statistics, and prevention research, said in an interview. “But I think it's worthwhile to look for reduced thyroid function in these women now. It's such an easy test to do, and the treatment is so cheap. I think it should be done.”
In an article published online in BMJ, two separate studies were reported (2009 Nov. 17 [doi:10.1136/bmj.b4336]). In the first Dr. Levine and his colleagues examined stored blood samples from a U.S. trial, Calcium for Preeclampsia Prevention, to check TSH levels early and later in pregnancy, in a comparison of 141 women who developed preeclampsia with 141 controls.
Whereas TSH did not vary significantly between the two groups early in pregnancy, by the time of delivery, those who developed preeclampsia had twice the risk of exhibiting high TSH levels, compared with controls.
Moreover, the increase in TSH level was significantly associated with increasing quartiles of soluble fms-like tyrosine kinase 1 (sFlt-1), which “may be responsible for the clinical phenotype of preeclampsia,” the investigators wrote.
In the second study, Dr. Levine and his colleagues analyzed the Norwegian Nord-Trondelag Health Study of 7,121 women who had given birth to a first child in 1967 or later, and measurements of thyroid function 20 or more years later. They found that those who had preeclampsia in their first pregnancy were 70% more likely to have high thyroid-stimulating hormone concentrations years later than were women who had not had preeclampsia. Those who had preeclampsia in two pregnancies had a nearly sixfold increased risk of high TSH levels.
“Increased circulating concentrations of [sFlt-1], most notably after onset of preeclampsia, were associated with subtle abnormalities of the thyroid during pregnancy. “These in turn may predispose to the development of reduced thyroid function and possibly overt hypothyroidism in later life,” they wrote.
“The hypothesis is fascinating and has to be explored further,” said Dr. Marshall D. Lindheimer, professor emeritus of obstetrics and gynecology and of medicine at the University of Chicago.