Incidence, Treatment, and Implications of Kidney Stones During Pregnancy: A Matched Population-Based Cohort Study

To determine the incidence of kidney stones in pregnancy, the risk of adverse birth outcomes, and treatment trends. We performed a population-based matched cohort study using Ontario's health care databases. All pregnancies in Ontario from 2004 to 2014 were identified. The study exposure was hospital admission, emergency room visit, or intervention for kidney stones during pregnancy. Each pregnancy with a stone was matched to up to six pregnancies without a stone based on age, region of residence, income quintile, year of cohort entry, prior births, and multibirths. The primary outcome was adverse birth outcome defined as preterm birth, low birth weight, or infant death. Secondary outcomes included premature rupture of membranes (PROM), pre-eclampsia, and cesarean section (C/S), as well as the type/frequency of intervention for stones in pregnancy. Logistic regression models, with generalized estimating equations, were used to assess any differences in study outcomes across groups. Of 1.39 million pregnancies identified, there were 2863 pregnancies with stones (0.2%), which were matched with 17,171 pregnancies without stones. Pregnancies with stones had an increased risk for adverse birth outcome compared with matched pregnancies without stones (odds ratio [OR] 1.62, confidence interval [95% CI] 1.43-1.82, p < 0.0001). Pregnancies with stones also had a greater risk for pre-eclampsia (OR 1.42, 95% CI 1.02-1.99, p = 0.04) and C/S (OR 1.39, 95% CI 1.27-1.51, p < 0.0001), but not PROM. Twenty-six percent of pregnant patients admitted for a stone had an intervention, most commonly a stent or ureteroscopy. Our study demonstrated an increased risk of adverse birth outcomes in pregnancies with kidney stones. These results will be important for counseling pregnant patients with kidney stones and women of reproductive age who are at risk of developing stones.