title: Incidence of appendicitis during pregnancy.
abstract: BACKGROUND
  The aetiology and pathogenesis of appendicitis remains unknown. A relation with female sex hormones has been proposed because of a lower incidence among women and incidence variations during the menstrual cycle, but studies have given inconsistent results. Pregnancy constitutes a period of dramatic increases in levels of female sex hormones, but the incidence of appendicitis during childbearing is not known.
  
  
  METHODS
  Case-control study of pregnancy status at the time of appendectomy of 53 058 women and of 53 058 population-based age-matched controls. Cases and controls were identified by linkage of the Swedish Inpatient Register and the nation-wide census. Pregnancy status at the time of operation was obtained by linkage with the Swedish Fertility Register. Differences in pregnancy status were analysed using conditional logistic regression and expressed as odds ratios (OR) with 95% CI.
  
  
  RESULTS
  Fewer patients than expected with appendicitis were pregnant compared with the controls, especially in the third trimester (OR = 0.49, 95% CI : 0.30-0.79 for perforated and OR = 0.33, 95% CI : 0.28-0.39 for non-perforated appendicitis).
  
  
  CONCLUSIONS
  The reduced incidence of appendicitis suggests a protective effect of pregnancy, especially in the third trimester.
authors.affiliation: Department of Surgery, County Hospital Ryhov, Jönköping, Sweden. roland.andersson@ryhov.ltjkpg.se
authors.forename: R E
authors.initials: RE
authors.lastname: Andersson
authors.forename: M
authors.initials: M
authors.lastname: Lambe
mesh_terms: D000328:Adult; D001062:Appendectomy; D001064:Appendicitis / Q000453:epidemiology* / Q000601:surgery; D016022:Case-Control Studies; D016009:Chi-Square Distribution; D005260:Female; D006801:Humans; D015994:Incidence; D016015:Logistic Models; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000453:epidemiology* / Q000601:surgery; D012042:Registries; D013548:Sweden / Q000453:epidemiology