Justification and objective There are several well-known anatomical and physiological changes during pregnancy that could contribute to kidney stone formation, but there is no evidence that they increase the risk of kidney stones during pregnancy. We determined whether there was an increased risk of first-time symptomatic kidney stones during and after pregnancy. Study design A population-based matched case-control study. Environment and participants 945 first-time symptomatic kidney stone-forming women aged 15 to 45 years and 1,890 age-matched control women in Olmsted County, MN, from 1984 to 2012. The index date was the date of onset of a symptomatic kidney stone both for the case as for the paired controls. Exposure The main exposure was pregnancy with assessment of risk variation at different time intervals before, during and after pregnancy. Medical records were manually reviewed to determine the conception and delivery dates of the pregnancies. Results Compared with nonpregnant women, the likelihood of symptomatic kidney stone formation 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), increased further during the third trimester (OR, 2.69; P = 0.001), peaked at 0 to 3 months postpartum (OR, 3.53; P < 0.001), and returned to baseline 1 year after delivery. These associations persisted after adjustment for age and race or for diabetes mellitus, hypertension, and obesity. These results did not differ significantly by age, race, time period, or number of previous pregnancies. Having a previous pregnancy (due date > 1 year 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 time of stone formation cannot be determined. Conclusions Pregnancy increases the risk of a symptomatic kidney stone for the first time. This risk peaks near delivery and then improves 1 year postpartum, although there is still a modest risk of kidney stones beyond 1 year postpartum. |
Mayo Clinic
Although researchers have long known that several physiological and anatomical changes occur during pregnancy that can contribute to kidney stone formation, evidence of the link is lacking. But now Mayo Clinic researchers believe they have that evidence.
An observational study that reviewed the medical records of nearly 3,000 female patients between 1984 and 2012 finds that pregnancy increases the risk of a symptomatic kidney stone for the first time. The risk peaks near delivery and then improves one year after delivery, although a modest risk of developing kidney stones continues beyond one year after delivery.
The study, published in the American Journal of Kidney Diseases , included 945 women who experienced a symptomatic kidney stone for the first time and 1,890 age-matched female control subjects. The goal of the study was to determine whether the risk of a first-time symptomatic kidney stone increased with pregnancy and whether the risk varied at different time periods before, during, and after pregnancy.
"We suspected that the risk of a kidney stone event would be high during pregnancy, but we were surprised that the risk remained high up to a year after delivery," says Andrew Rule, MD, a Mayo Clinic nephrologist and lead author of the study. "There is also a slightly increased risk of a kidney stone event beyond one year after delivery. This finding implies that while most kidney stones that form during pregnancy are detected early by the painful passage, some may remain stable in the kidney undetected for a longer period before detaching and resulting in a painful passage."
A symptomatic kidney stone event is the most common non-obstetric hospital admission diagnosis for pregnant women. A symptomatic kidney stone event occurs in 1 in every 250-1,500 pregnancies, research shows, and occurs most frequently during the second and third trimesters. Kidney stones, although rare, can cause significant complications, ranging from preeclampsia and urinary tract infection to premature labor and delivery and pregnancy loss.
Diagnosing kidney stones during pregnancy can be challenging, given limited imaging options due to concerns about radiation exposure, says Dr. Rule . Treatment may also be complicated by obstetric concerns.
Several physiological reasons may contribute to why pregnancy contributes to kidney stone formation, says Charat Thongprayoon, MD, a Mayo Clinic nephrologist and corresponding author of the study. During pregnancy, ureteral compression and ureteral relaxation due to elevated progesterone hormone can cause urinary stasis in the body. Additionally, increased urinary calcium excretion and elevated urine pH during pregnancy can lead to the formation of calcium phosphate stones.
Awareness of an increased risk of kidney stones during pregnancy and the postpartum period can help healthcare providers offer diagnostic and prevention strategies for women.
"Urinary obstruction due to kidney stones can cause pain that some patients describe as the worst pain they have ever experienced," says Dr. Thongprayoon. "During pregnancy, a kidney stone can contribute to a 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 the obesity".
General dietary recommendations to prevent kidney stone disease include high fluid intake and a low-salt diet. Mayo Clinic experts also recommend adequate calcium intake during pregnancy of at least 1,000 milligrams per day, preferably from dietary sources such as dairy products rather than calcium supplements.
The research examined data from the Rochester Epidemiology Project, a collaboration of clinics, hospitals and other health care facilities in Minnesota and Wisconsin, and community members who have agreed to share their medical records for research. This project enables vital research that can find causes, treatments and cures for diseases. It is supported by the National Institutes of Health, the US Public Health Service, and the National Center for Advancing Translational Sciences.
