Risk of Symptomatic Kidney Stones During and After Pregnancy

Abstract

Rationale & objective: There are several well-known anatomical and physiological changes during pregnancy that could contribute to kidney stone formation, but evidence that they increase the risk of kidney stones during pregnancy is lacking. We determined whether there was an increased risk of a first-time symptomatic kidney stone during and after pregnancy.

Study design: A population-based matched case-control study.

Setting & participants: 945 female first-time symptomatic kidney stone formers aged 15-45 years and 1,890 age-matched female controls in Olmsted County, MN, from 1984-2012. The index date was the date of onset of a symptomatic kidney stone for both the case and her matched controls.

Exposure: The primary exposure was pregnancy with assessment for variation in risk across different time intervals before, during, and after pregnancy. Medical records were manually reviewed to determine the conception and delivery dates for pregnancies.

Outcome: Medical record-validated first-time symptomatic kidney stone.

Analytical approach: Conditional and unconditional multivariable logistic regression analysis.

Results: Compared with nonpregnant women, the odds of a symptomatic kidney stone forming in women was similar in the first trimester (OR, 0.92; P=0.8), began to increase during the second trimester (OR, 2.00; P=0.007), further increased during the third trimester (OR, 2.69; P=0.001), peaked at 0 to 3 months after delivery (OR, 3.53; P<0.001), and returned to baseline by 1year after delivery. These associations persisted after adjustment for age and race or for diabetes mellitus, hypertension, and obesity. These results did not significantly differ by age, race, time period, or number of prior pregnancies. Having a prior pregnancy (delivery date>1year ago) was also associated with a first-time symptomatic kidney stone (OR, 1.27; P=0.01).

Limitations: Observational study design in a predominantly White population. The exact timing of stone formation cannot be determined.

Conclusions: Pregnancy increases the risk of a first-time symptomatic kidney stone. This risk peaks close to delivery and then improves by 1 year after delivery, though a modest risk of a kidney stone still exists beyond 1 year after delivery.

Keywords: Computed tomography (CT); hydronephrosis; imaging; kidney stones; nephrolithiasis; obstetric complications; population-based; pregnancy; recurrence; stone composition; symptoms; ultrasound.

Figure 1.

Timing of index date (date of symptom onset for stone formers) in relation to pregnancy

Figure 2.

Case-control study design. Index date is the date of onset of a symptomatic kidney stone for both the case and their matched controls. There were 175 (18.5%) stone formers and 174 (9.2%) controls whose index dates occurred between 2^nd trimester and 1 year after delivery.

Figure 3.

Odds ratios for first-time symptomatic kidney stone formers versus control relative to date of conception (time 0=reference value). Black line (odds ratio) is estimated using a restricted cubic spline with six knots and shown from 5 months prior to conception to 23 months after conception. Grey areas represent 95% confidence limits. Dashed line is set at odds ratio=1.