title: Nephrolithiasis and pregnancy: has the incidence been rising?
abstract: BACKGROUND
  The incidence of nephrolithiasis has consistently been increasing over recent decades. This has been attributed to diet, obesity, environmental temperature changes, and comorbid diseases such as diabetes. Incidence change has not been studied in the pregnant population. Herein, we report our experience with stone diagnosis in this unique patient population over the past 2 decades.
  
  
  METHODS
  Hospital data from a tertiary women's hospital were examined for international classification of diseases, ninth revision (ICD-9) codes for pregnancy (640-648, V22.0, V22.1, V22.2), and urolithiasis (592.0, 592.1, 592.9) between 1991 and 2011. The change in incidence in nephrolithiasis, pregnancy, and the combination of both was examined.
  
  
  RESULTS
  In the 21-year period studied, 876 pregnant patients were given a diagnosis of nephrolithiasis at our hospital. Over the same time, 204,034 pregnant patients and 3262 patients with stones were treated. Comparing patients seen from 1991-2000 to those seen from 2001-2011 revealed a significant increase in patients with stones (78 vs. 226/year, p=0.004), but no change in pregnant patients (9467 vs. 9942/year, p=0.3) or pregnant patients with stones (36 vs. 47, p=0.1). Evaluating patients at 5-year intervals confirmed the expected increase in patients with stones, but no change in incidence of nephrolithiasis in pregnant patients was noted.
  
  
  CONCLUSIONS
  There was no change in incidence of nephrolithiasis in pregnant patients over a 2-decade period. Further research is warranted to determine why the pregnant population does not have the expected increase in nephrolithiasis. Larger, multi-institutional studies are needed to validate our results.
authors.affiliation: 1 Department of Urology, University of Pittsburgh Medical Center , Pittsburgh, Pennsylvania.
authors.forename: Julie M
authors.initials: JM
authors.lastname: Riley
authors.forename: Anne G
authors.initials: AG
authors.lastname: Dudley
authors.forename: Michelle Jo
authors.initials: MJ
authors.lastname: Semins
mesh_terms: D000328:Adult; D005260:Female; D005544:Forecasting; D006801:Humans; D015994:Incidence; D053040:Nephrolithiasis / Q000453:epidemiology*; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology*; D012189:Retrospective Studies; D014481:United States / Q000453:epidemiology; D055815:Young Adult