title: Population differences and the effect of vaginal progesterone on preterm birth in women with threatened preterm labor (.).
abstract: OBJECTIVE
  Threatened preterm labor (tPTL) is a complication of pregnancy. Identification of women and clinical definition differs between countries. This study investigated differences in tPTL and effectiveness of vaginal progesterone to prevent preterm birth (PTB) between two countries.
  
  
  METHODS
  Secondary analysis of a randomized controlled trial (RCT) from Argentina and Switzerland comparing vaginal progesterone to placebo in women with tPTL (n = 379). Cox proportional hazards analysis was performed to compare placebo groups of both countries and to compare progesterone to placebo within each country. We adjusted for baseline differences. Iatrogenic onset of labor or pregnancy beyond gestational age of interest was censored.
  
  
  RESULTS
  Swiss and Argentinian women were different on baseline. Risks for delivery <14 days and PTB < 34 and < 37 weeks were increased in Argentina compared to Switzerland, HR 3.3 (95% CI 0.62-18), 54 (95% CI 5.1-569) and 3.1 (95% CI 1.1-8.4). In Switzerland, progesterone increased the risk for delivery <14 days [HR 4.4 (95% CI 1.3-15.7)] and PTB <37 weeks [HR 2.5 (95% CI 1.4-4.8)], in Argentina there was no such effect.
  
  
  CONCLUSIONS
  In women with tPTL, the effect of progesterone may vary due to population differences. Differences in populations should be considered in multicenter RCTs.
authors.affiliation: a Department of Obstetrics and Gynaecology , Academic Medical Center , Amsterdam , the Netherlands .
authors.forename: Frederik Jan Robin
authors.initials: FJ
authors.lastname: Hermans
authors.affiliation: b Centro De Investigación En Salud Poblacional - CISAP - (Population Health Research Center), Hospital GA Carlos G Durand , Buenos Aires , Argentina .
authors.forename: Ariel
authors.initials: A
authors.lastname: Karolinski
authors.affiliation: c Department of Obstetrics and Gynaecology , Geneva University Hospitals and University of Geneva Faculty of Medicine , Geneva , Switzerland .
authors.forename: Véronique
authors.initials: V
authors.lastname: Othenin-Girard
authors.affiliation: b Centro De Investigación En Salud Poblacional - CISAP - (Population Health Research Center), Hospital GA Carlos G Durand , Buenos Aires , Argentina .
authors.forename: María Victoria
authors.initials: MV
authors.lastname: Bertolino
authors.affiliation: a Department of Obstetrics and Gynaecology , Academic Medical Center , Amsterdam , the Netherlands .|d Julius Center for Healthcare Research and Primary Care, University Medical Center Utrecht , Utrecht , the Netherlands .|e Stanford Prevention Research Center, Stanford University , Stanford , CA , USA .
authors.forename: Ewoud
authors.initials: E
authors.lastname: Schuit
authors.affiliation: b Centro De Investigación En Salud Poblacional - CISAP - (Population Health Research Center), Hospital GA Carlos G Durand , Buenos Aires , Argentina .
authors.forename: Pablo
authors.initials: P
authors.lastname: Salgado
authors.affiliation: f Department of Obstetrics and Gynaecology , University Hospital, University Basel , Basel , Switzerland .
authors.forename: Irene
authors.initials: I
authors.lastname: Hösli
authors.affiliation: c Department of Obstetrics and Gynaecology , Geneva University Hospitals and University of Geneva Faculty of Medicine , Geneva , Switzerland .
authors.forename: Olivier
authors.initials: O
authors.lastname: Irion
authors.affiliation: g Department of Obstetrics and Gynaecology , Hospital Materno Infantil Ramón Sardá , Buenos Aires , Argentina .
authors.forename: Cristina
authors.initials: C
authors.lastname: Laterra
authors.affiliation: h The Robinson Research Institute, School of Medicine, University of Adelaide , Adelaide , Australia , and.|i The South Australian Health and Medical Research Institute , Adelaide , Australia.
authors.forename: Ben Willem J
authors.initials: BW
authors.lastname: Mol
authors.affiliation: c Department of Obstetrics and Gynaecology , Geneva University Hospitals and University of Geneva Faculty of Medicine , Geneva , Switzerland .
authors.forename: Begoña
authors.initials: B
authors.lastname: Martinez de Tejada
mesh_terms: D000328:Adult; D001118:Argentina; D016009:Chi-Square Distribution; D004311:Double-Blind Method; D005260:Female; D005865:Gestational Age; D006801:Humans; D007752:Obstetric Labor, Premature / Q000188:drug therapy*; D011247:Pregnancy; D047928:Premature Birth / Q000517:prevention & control*; D011374:Progesterone / Q000627:therapeutic use*; D011372:Progestins / Q000627:therapeutic use*; D016016:Proportional Hazards Models; D018709:Statistics, Nonparametric; D013557:Switzerland; D055815:Young Adult
chemical_list: D011372:Progestins; D011374:Progesterone
keywords: Harm; population differences; preterm birth; randomized controlled trial; secondary analysis; selection criteria; threatened preterm labor; treatment effect; treatment interaction; vaginal progesterone