Study Finds Risk of Kidney Stones Increases During and Immediately After Pregnancy

Andrew Rule, MD

Pregnancy could increase a woman’s risk of developing kidney stones, according to the results of a recent study from the Mayo Clinic.

The study, which examined data from nearly 3000 women over a 28-year period, found pregnancy increases the risk of a first-time symptomatic kidney stone and also returned evidence suggesting this risk lasts up to a year after giving birth.

"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," said the study’s senior investigator Andrew Rule, MD, a nephrologist at the Mayo Clinic in Minnesota, in a statement. "There also remains a slightly increased risk of a kidney stone event beyond a year after delivery. This finding implies that 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 resulting in a painful passage."

With the aim of improving the care of women during and after pregnancy, investigators sought to fill the apparent knowledge gap related to risk of kidney stones during pregnancy. Using data from women within the Rochester Epidemiology Project, investigators identified 2835 females aged 15-45 years for inclusion in their analysis.

Briefly, the Rochester Epidemiology Project is a medical records-linkage system created in 1966 designed to capture medical care within Olmsted County, Minnesota. For the current analysis, 945 women with first-time symptomatic kidney stones between 1984-2012 were aged-matched in a 1:2 ratio to 1890 with no history of kidney stones.

ICD-9/10 codes were used to identify women who formed kidney stones during the study period. These codes were also used to determine presence of diabetes, hypertension, chronic kidney disease, obesity, gout, and smoking history among study participants.

The investigators planned to use logistic regression analysis to calculate the odds of developing a kidney stone during multiple time periods before, during, and after pregnancy. These time periods included the first, second, and third trimester, as well as 0-6 months prior to conception and 3 months, 3-6, 6-9, 9-12, and 12-24 months after delivery.

When compared to non-pregnant women, the odds of a symptomatic kidney stone were similar during the first trimester (OR, 0.92; 95% CI, 0.45-1.86; P=.81), but this risk began to increase during the second (OR, 2.0; 95% CI, 1.21-3.22; P=.007) and third trimester (OR, 2.69; 95% CI, 1.49-4.84; P=.001). Results indicated the risk for kidney stones peak during the time period 0-3 months after delivery (OR, 3.53; 95% CI, 2.14-5.56; P <.001), but return to baseline at 1-year post-delivery (OR, 1.03; 95% CI, 0.70-1.53; P=.9).

Further analysis indicated these associations persisted after adjustment for age and race or for the presence of diabetes mellitus, hypertension, or obesity. Additionally, the results of the study did not significantly differ by age, race, time period, or number of prior pregnancies. However, investigators did find having a prior pregnancy with a delivery date less than 1 year before was associated with a first-time symptomatic kidney stone (OR, 1.27; P=.01).

“During pregnancy, a kidney stone may contribute to serious complication, and 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,” noted lead investigator Charat Thongprayoon, MD, a nephrologist at the Mayo Clinic in Minnesota, in the aforementioned statement.

This study, “The risk of a symptomatic kidney stone during and after pregnancy,” was published in the American Journal of Kidney Diseases.