title: Maternal and pregnancy characteristics and risk of infantile hypertrophic pyloric stenosis.
abstract: OBJECTIVE
  The incidence of infantile hypertrophic pyloric stenosis (IHPS) in Sweden decreased dramatically during the 1990s. The aim of the study was to examine IHPS risk factors and the possible change in them as the incidence declined.
  
  
  METHODS
  This is a case-control study including 3608 surgically treated IHPS cases and 17588 matched controls during 1973-2008. Cases were identified in the Swedish National Patient Register and data on possible risk factors were collected from the Swedish Medical Birth Register. The association between study variables and IHPS was analyzed using conditional logistic regression for the whole study period and separately for periods with high and low IHPS incidences.
  
  
  RESULTS
  Prematurity (OR, 2.54; 95% CI, 2.06-3.14), caesarean delivery (OR, 1.67; 95% CI, 1.51-1.86), maternal smoking (OR, 1.82; 95% CI, 1.53-2.16), and young maternal age (< 20yrs) (OR, 1.42; 95% CI, 1.17-1.73) were associated with an increased IHPS risk. Birth order 2 (OR, 0.78; 95% CI, 0.71-0.85) or more was associated with a lower IHPS risk. ORs for smoking increased at low incidence rate.
  
  
  CONCLUSIONS
  We report caesarean section, prematurity, primiparity, young maternal age, and smoking as significant IHPS risk factors. The impact of smoking was higher during periods with a low incidence.
authors.affiliation: Department of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden; Division of Paediatric Surgery, Astrid Lindgren Children's Hospital, Stockholm, Sweden. Electronic address: anna.svenningsson@ki.se.
authors.forename: Anna
authors.initials: A
authors.lastname: Svenningsson
authors.affiliation: Clinical Epidemiology Unit, Department of Medicine, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Tobias
authors.initials: T
authors.lastname: Svensson
authors.affiliation: Clinical Epidemiology Unit, Department of Medicine, Karolinska Institutet, Stockholm, Sweden; Division of Urology, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Olof
authors.initials: O
authors.lastname: Akre
authors.affiliation: Department of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden; Division of Paediatric Surgery, Astrid Lindgren Children's Hospital, Stockholm, Sweden.
authors.forename: Agneta
authors.initials: A
authors.lastname: Nordenskjöld
mesh_terms: D000328:Adult; D002585:Cesarean Section / Q000009:adverse effects*; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008423:Maternal Age; D011247:Pregnancy; D011379:Prognosis; D046248:Pyloric Stenosis, Hypertrophic / Q000453:epidemiology / Q000209:etiology*; D018570:Risk Assessment; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult
keywords: Caesarean section; Epidemiology; Prematurity; Pyloric stenosis; Smoking