Pregnancy Increases Risk for Symptomatic Kidney Stone

Pam Harrison

April 28, 2021

Pregnancy increases the risk for first-time symptomatic kidney stone formation which peaks close to the time of delivery but can persist even a year later, a population-based, case-controlled study suggests.

"We suspected the risk of a kidney stone event would be high during pregnancy, but we were surprised that the risk remained high for up to a year after delivery," senior author Andrew Rule, MD, a nephrologist at Mayo Clinic, Rochester, Minnesota, said in a statement from his institution.

"[So] while most kidney stones that form during pregnancy are detected early by painful passage, some may remain stable in the kidney undetected for a longer period before dislodging and [again] resulting in a painful passage," he added.

The study was published online April 15 in The American Journal of Kidney Diseases by Charat Thongprayoon, MD, also of the Mayo Clinic, and colleagues.

"The results of this study indicate that prenatal counseling regarding kidney stones may be warranted, especially for women with other risk factors for kidney stones, such as obesity," he noted.

First-Time Stone Formers

The observational study included 945 first-time symptomatic kidney stone formers between 15 and 45 years of age who were compared with 1890 age-matched female controls from the Rochester Epidemiology Project. The latter is a medical record linkage system for almost all medical care administered in Olmsted County, Minnesota.

Compared with nonpregnant women, the odds of a symptomatic kidney stone forming in a pregnant woman was similar in the first trimester (odds ratio, 0.92; P = .8), began to increase during the second trimester (OR, 2.00; P = .007), further increased during the third trimester (OR, 2.69; P = .001), and peaked at 0 to 3 months after delivery (OR, 3.53; P < .001). The risk returned to baseline by 1 year after delivery.

These associations persisted after adjustment for age and race or for diabetes, hypertension, and obesity. These results did not significantly differ by age, race, time period, or number of prior pregnancies.

The risk of a pregnant woman developing a symptomatic kidney stone was higher in women with obesity compared with those of normal weight (P = .01).

And compared with women who had not been pregnant before, one prior pregnancy also increased the risk of having a symptomatic kidney stone by approximately 30% (OR, 1.29; P = .03), although two or more prior pregnancies did not significantly increase symptomatic kidney stone risk.

Thus, "it can be inferred that the odds of a symptomatic kidney stone peak around the time of delivery," the authors emphasize.

"The odds of a first-time symptomatic kidney stone then decreased over time and were fully attenuated and no longer statistically significant by 12 months after delivery," the authors add.

Thongprayoon says there are several physiologic reasons why pregnancy might contribute to kidney stone formation.

During pregnancy, ureteral compression and ureteral relaxation due to elevated progesterone levels can cause urinary stasis.

Furthermore, increased urinary calcium excretion and elevated urine pH during pregnancy can promote calcium phosphate stone formation. It is noteworthy that almost all pregnant, first-time stone formers had calcium phosphate stones.

"During pregnancy, a kidney stone may contribute to serious complications," Thongprayoon explained.

General dietary recommendations for preventing kidney stones include drinking abundant fluids and consuming a low-salt diet.

The study was supported by the Mayo Clinic O'Brien Urology Research Center and a grant from the National Institute of Diabetes and Digestive and Kidney Diseases. The authors have disclosed no relevant financial relationships.

Am J Kidney Dis. Published online April 15, 2021. Abstract

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