title: Changes in incidence of iatrogenic and spontaneous preterm births over time: a population-based study.
abstract: OBJECTIVE
  To examine the proportion of iatrogenic births among all preterm births over a 26-year period.
  
  
  METHODS
  A registry-based survey of preterm deliveries between 1987 and 2012 analyzed by the onset of labor: spontaneous with intact membranes, preterm premature rupture of membranes (PPROM) or iatrogenic. Stratification into categories by gestation (22 weeks to 27 weeks and 6 days, 28 weeks to 31 weeks and 6 days, 32 weeks to 33 weeks and 6 days, 34 weeks to 36 weeks and 6 days) was performed. Preterm birth rates were analyzed using the Mantel-Haenszel linear-by-linear association χ2-test (P<0.05 significant). Logistic regression was used to account for potential confounders.
  
  
  RESULTS
  Overall preterm birth rate was 5.9% (31328 deliveries) including 2358 (0.4%) before 28 completed weeks, 3388 (0.6%) between 28 weeks and 31 weeks 6 days, 3970 (0.8%) between 32 weeks and 33 weeks and 6 days, and 21611 (4.1%) between 34 weeks and 36 weeks and 6 days There was an increase in overall preterm birth rate (P<0.001). The rate of iatrogenic preterm births and PPROM increased over time (P<0.001 and P<0.014, respectively). Rates of spontaneous preterm birth decreased (P<0.001). After accounting for potential confounders, year of birth remained an independent risk factor for iatrogenic preterm delivery in all four gestational age categories (P<0.001).
  
  
  CONCLUSIONS
  The incidence of iatrogenic preterm birth is increasing with a concomitant decrease in the incidence of spontaneous preterm birth. Attempts to analyze, interpret and decrease preterm birth rates should consider spontaneous and iatrogenic preterm births separately.
authors.forename: Miha
authors.initials: M
authors.lastname: Lucovnik
authors.forename: Andreja Trojner
authors.initials: AT
authors.lastname: Bregar
authors.forename: Lili
authors.initials: L
authors.lastname: Steblovnik
authors.forename: Ivan
authors.initials: I
authors.lastname: Verdenik
authors.forename: Ksenija
authors.initials: K
authors.lastname: Gersak
authors.forename: Isaac
authors.initials: I
authors.lastname: Blickstein
authors.forename: Natasa
authors.initials: N
authors.lastname: Tul
mesh_terms: D005260:Female; D005322:Premature Rupture of Fetal Membranes / Q000453:epidemiology; D005865:Gestational Age; D006801:Humans; D007049:Iatrogenic Disease / Q000453:epidemiology; D015994:Incidence; D007231:Infant, Newborn; D007234:Infant, Premature; D016015:Logistic Models; D008297:Male; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology*; D012042:Registries; D012189:Retrospective Studies; D012307:Risk Factors; D017524:Slovenia / Q000453:epidemiology