Link found between preeclampsia and reduced thyroid function

Preeclampsia may be associated with subclinical hypothyroidism during pregnancy and appears to predispose women to reduced thyroid function up to 20 years after pregnancy, according to recently published data in BMJ.

Researchers conducted the Calcium for Preeclampsia Prevention trial, a nested case-control study during pregnancy from 1992 to 1995, and the Nord-Trondelag Health Study, a Norwegian population-based study during 1995 to 1997. The study populations included 141 women with preeclampsia and 141 normotensive controls from the Calcium for Preeclampsia Prevention trial and 7,121 women in the Nord-Trondelag Health Study who first gave birth in 1967 or later.

Baseline serum levels were measured at 21 weeks of gestation for women in the Calcium for Preeclampsia Prevention Trial, and the levels were measured again after onset of preeclampsia. Thyroid-stimulating hormone levels increased 2.42 times above baseline compared with a 1.48-fold increase in the control group.

Women with preeclampsia had a greater decrease in free triiodothyronine compared with controls (case ratio to control ratio, 0.96; 95% CI, 0.92-0.99). Predelivery specimens from women with preeclampsia were also more likely to have TSH concentrations above the reference range compared with controls (adjusted OR=2.2; 95% CI, 1.1-4.4). Despite the absence of other hypothyroidism levels, one of every four of the women with preeclampsia had TSH levels above normal compared with one out of every seven controls.

In all women, increasing TSH concentration was associated with an increase in predelivery soluble fms-like tyrosine kinase 1, a molecule in the blood believed to cause preeclampsia symptoms (P=.002 for trend in women with preeclampsia and P<.001 in controls).

Reduced thyroid function later in life

In the Norwegian study, women who had a history of preeclampsia in their first pregnancy were 1.7 times more likely to have TSH concentrations above the reference range of 3.5 mIU/I compared with controls. Women with preeclampsia in their first and second pregnancies were nearly six times more likely to have high TSH levels.

A history of preeclampsia was also associated with high TSH concentrations without thyroid peroxidase antibodies (adjusted OR=2.6; 95% CI, 1.3-5.0). The researchers wrote that this finding suggests hypothyroidism without an autoimmune process and noted that it was most significant for women who had preeclampsia in both their first and second pregnancies (adjusted OR=5.8; 95% CI, 1.3-25.5).

The researchers wrote that these findings could have implications on the care of women with preeclampsia. In addition to monitoring these women for cardiovascular and renal disease, physicians might now consider monitoring them for reduced thyroid function.

Levine RJ. BMJ. 2009;339:b4336.