Association of Pregnancy with Stone Formation among Women in the United States: A NHANES Analysis 2007 to 2012

Purpose: Lithogenic urinary changes develop during pregnancy. Such changes may increase stone proclivity thereafter in working and child rearing aged women. However, to our knowledge such an association has not been previously identified. Materials and Methods: We analyzed nationally representative data from the 2007 to 2012 NHANES (National Health and Nutrition Examination Survey) to assess the association between pregnancy and nephrolithiasis. Results: The weighted national prevalence of nephrolithiasis among women 50 years or younger was 6.4% (95% CI 5.4-7.6). The prevalence of nephrolithiasis was significantly higher among women who had been pregnant compared with those who had never been pregnant (7.5% vs 3.2%, p = 0.0004). On univariate regression those who had been pregnant had more than twice the odds of having had kidney stones (OR 2.44, 95% CI 1.50-3.98). An increased likelihood of nephrolithiasis in those with a history of pregnancy persisted on multivariable logistic regression adjusting for age, ethnicity, obesity, history of diabetes, gout, hormone use, water intake and high sodium diet (OR 2.13, 95% CI 1.31-3.45). Finally, the adjusted prevalence of nephrolithiasis increased significantly with an increasing number of pregnancies from 5.2% in those with 0 reported pregnancies to 12.4% in those with 3 or more pregnancies (p = 0.001). Conclusions: Nephrolithiasis is strongly associated with prior pregnancies. Among women of reproductive age the odds of stones are greater than doubled in those who had been pregnant compared with those who had never been pregnant. Nephrolithiasis prevalence also increases with the increasing number of pregnancies. Future investigation and identification of modifiable risk factors among pregnant patients may allow for a reduction in the burden of stone disease in women.