Confounders Obscure Link between Preeclampsia and ESRD

The roles of obesity and pre-existing kidney disease make it difficult to assess the true nature of the association between preeclampsia and end stage renal disease (ESRD), concludes a report in the American Journal of Kidney Diseases.

The researchers used the US Renal Data System to identify 34,581 women who gave birth in Olmsted County, Minn., between 1976 and 2010. Forty-four women with confirmed ESRD were matched for year of birth, age at first pregnancy, and parity to two controls. In the cases, median time from last pregnancy to ESRD onset was 17.7 years.

Pregnancies affected by preeclampsia were confirmed by review of medical records. The association between preeclampsia and ESRD was analyzed, with attention to shared risk factors such as previous kidney disease, obesity, diabetes, and hypertension.

Nine of the 44 women with ESRD had evidence of kidney disease before their first pregnancy, a rate of 21%, compared to just 1 of 88 controls. Medical records review identified preeclampsia in 18% of cases versus 5% of controls, for an unadjusted odds ratio of 4.0. The association between preeclampsia and ESRD was unaffected by adjustment for race, education, diabetes, and hypertension before pregnancy. However, it was weakened and became nonsignificant after adjustment for obesity.

Registry-based studies have suggested that hypertensive disorders of pregnancy are a risk factor for ESRD. However, because of shared risk factors, the nature of the association between these two conditions has been unclear.

The new study suggests a fourfold increase in ESRD associated with preeclampsia. However, it also provides evidence of a possible confounding effect of obesity. In addition, 20% of women with ESRD already had evidence of kidney disease before their first pregnancy. While the causal pathway is still unclear, the researchers conclude: “Preeclampsia may identify women early in life who are at future risk for kidney disease” [Kattah AG, et al. Preeclampsia and ESRD: the role of shared risk factors. Am J Kidney Dis 2017; 69:498–505].