title: The effect of cerclage in twin gestations with short cervix: a Bayesian evaluation.
abstract: OBJECTIVE
  Bayesian inference allows the revision of prior clinical estimates of treatment effectiveness based on current data. We apply it to a published dataset evaluating the effect of cerclage upon preterm delivery in twin gestations with a short cervix.
  
  
  METHODS
  Prior probability distributions for delivery <35 weeks gestation for the control group and the treatment (cerclage) group were constructed under assumptions ranging from treatment having no effect (prior A) to halving early deliveries (prior C). Likelihood functions were calculated based on a published meta-analysis. Posterior probability densities were derived from which risk ratios for early delivery were computed, with 95% credible intervals and the probability of cerclage benefit.
  
  
  RESULTS
  Median posterior risk ratios (95% credible intervals) for delivery <35 weeks with cerclage are 1.51 (1.02-2.33) for prior A and 1.11 (0.72-1.77) for prior C. The probability of cerclage benefit ranged from 2.1% for prior A to 31.4% for prior C. By comparison, the conventional risk ratio (95% confidence interval) for early delivery, based on the data alone, is 2.08 (1.18-3.69).
  
  
  CONCLUSIONS
  As might be anticipated, those with low expectation of cerclage benefit remain more convinced of the ineffectiveness (or harm) of the procedure than those with higher expectations.
authors.affiliation: Maternal-Fetal Medicine Consultant, St. Joseph Health Center , St. Charles, MO , USA .
authors.forename: William L
authors.initials: WL
authors.lastname: Holcomb
authors.forename: Erol
authors.initials: E
authors.lastname: Amon
authors.forename: James H
authors.initials: JH
authors.lastname: Albert
mesh_terms: D001499:Bayes Theorem; D023802:Cerclage, Cervical / Q000009:adverse effects / Q000706:statistics & numerical data; D054791:Cervical Length Measurement / Q000706:statistics & numerical data; D002584:Cervix Uteri / Q000473:pathology* / Q000601:surgery; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000453:epidemiology*; D059285:Pregnancy, Twin / Q000706:statistics & numerical data*; D016896:Treatment Outcome; D014427:Twins; D002581:Uterine Cervical Incompetence / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000601:surgery*
keywords: Multiple gestations; preterm delivery; prevention; statistics