title: Is it possible to estimate the minimal clinically important treatment effect needed to change practice in preterm birth prevention? Results of an obstetrician survey used to support the design of a trial.
abstract: BACKGROUND
  Sample sizes for obstetrical trials are often based on the opinion of investigators about clinically important effect size. We surveyed Canadian obstetricians to investigate clinically important effect sizes required before introducing new treatments into practice to prevent preterm birth.
  
  
  METHODS
  Questionnaires were mailed to practicing obstetricians, asking the magnitude of pregnancy prolongation required to introduce treatments into practice. The three prophylactic treatments were of increasing invasiveness: vaginal progesterone, intramuscular progesterone, and cervical cerclage. We also asked about the perceived most relevant outcome measures for obstetrical trials and current obstetrical practice in preterm birth prevention.
  
  
  RESULTS
  544/1293(42.1%) completed questionnaires were received. The majority of respondents required one or two weeks' increase in length of gestation before introducing vaginal (372,77.1%), and intramuscular progesterone(354,67.9%). At least three weeks increase was required before introducing prophylactic cervical cerclage(326,62.8%). Clinicians who already used a treatment required a smaller difference before introducing it into practice. Decreasing neonatal morbidity was cited as the most important outcome for obstetrical trials (349,72.2%).
  
  
  CONCLUSIONS
  Obstetricians would require a larger increase in treatment effect before introducing more invasive treatments into practice. Although infant morbidity was perceived as a more important outcome, clinicians appeared willing to change practice on the basis of prolongation of pregnancy, a surrogate outcome. We found that there is not a single minimum clinically important treatment effect that will influence all practising clinicians: rather the effect size that will influence physicians is affected by the nature of the treatment, the reported outcome measure and the clinician's own current clinical practice.
authors.affiliation: Department of Obstetrics and Gynaecology, University of Calgary, Calgary, Canada. sue.ross@albertahealthservices.ca
authors.forename: Sue
authors.initials: S
authors.lastname: Ross
authors.forename: Jill
authors.initials: J
authors.lastname: Milne
authors.forename: Shannon
authors.initials: S
authors.lastname: Dwinnell
authors.forename: Selphee
authors.initials: S
authors.lastname: Tang
authors.forename: Stephen
authors.initials: S
authors.lastname: Wood
mesh_terms: D000282:Administration, Intravaginal; D002170:Canada; D023802:Cerclage, Cervical / Q000379:methods; D002986:Clinical Trials as Topic; D003657:Decision Making; D019317:Evidence-Based Medicine; D005260:Female; D006801:Humans; D007273:Injections, Intramuscular; D009774:Obstetrics / Q000592:standards*; D010820:Physicians / Q000523:psychology* / Q000706:statistics & numerical data; D010818:Practice Patterns, Physicians'; D011247:Pregnancy; D011256:Pregnancy Outcome; D011272:Pregnancy, Multiple; D011273:Pregnancy, Prolonged / Q000517:prevention & control; D047928:Premature Birth / Q000188:drug therapy / Q000517:prevention & control*; D011374:Progesterone / Q000008:administration & dosage / Q000627:therapeutic use; D016032:Randomized Controlled Trials as Topic / Q000379:methods / Q000706:statistics & numerical data; D012107:Research Design; D018401:Sample Size; D011795:Surveys and Questionnaires
chemical_list: D011374:Progesterone