title: A multivariable model to guide the decision for pessary placement to prevent preterm birth in women with a multiple pregnancy: a secondary analysis of the ProTWIN trial.
abstract: OBJECTIVE
  The ProTWIN Trial (NTR1858) showed that, in women with a multiple pregnancy and a cervical length < 25(th) percentile (38 mm), prophylactic use of a cervical pessary reduced the risk of adverse perinatal outcome. We investigated whether other maternal or pregnancy characteristics collected at baseline can improve identification of women most likely to benefit from pessary placement.
  
  
  METHODS
  ProTWIN is a multicenter randomized trial in which 808 women with a multiple pregnancy were assigned to pessary or control. Using these data we developed a multivariable logistic model comprising treatment, cervical length, chorionicity, pregnancy history and number of fetuses, and the interaction of these variables with treatment as predictors of adverse perinatal outcome.
  
  
  RESULTS
  Short cervix, monochorionicity and nulliparity were predictive factors for a benefit from pessary insertion. History of previous preterm birth and triplet pregnancy were predictive factors of possible harm from pessary. The model identified 35% of women as benefiting (95% CI, 32-39%), which is 10% more than using cervical length only (25%) for pessary decisions. The model had acceptable calibration. We estimated that using the model to guide the choice of pessary placement would reduce the risk of adverse perinatal outcome significantly from 13.5% when no pessary is inserted to 8.1% (absolute risk reduction, 5.4% (95% CI, 2.1-8.6%)).
  
  
  CONCLUSIONS
  We developed and internally validated a multivariable treatment selection model, with cervical length, chorionicity, pregnancy history and number of fetuses. If externally validated, it could be used to identify women with a twin pregnancy who would benefit from a pessary, and lead to a reduction in adverse perinatal outcomes in these women. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.
authors.affiliation: Department of Obstetrics and Gynaecology, Academic Medical Centre, Amsterdam, The Netherlands.|Department of Clinical Epidemiology, Biostatistics and Bioinformatics, Academic Medical Centre, Amsterdam, The Netherlands.
authors.forename: P
authors.initials: P
authors.lastname: Tajik
authors.affiliation: Department of Obstetrics and Gynaecology, Atrium Medical Centre, Heerlen, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: Monfrance
authors.affiliation: Department of Obstetrics and Gynaecology, Academic Medical Centre, Amsterdam, The Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: van 't Hooft
authors.affiliation: Department of Obstetrics and Gynaecology, Academic Medical Centre, Amsterdam, The Netherlands.
authors.forename: S M S
authors.initials: SM
authors.lastname: Liem
authors.affiliation: Department of Obstetrics and Gynaecology, Academic Medical Centre, Amsterdam, The Netherlands.|Julius Centre for Health Sciences and Primary Care, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: E
authors.initials: E
authors.lastname: Schuit
authors.affiliation: Department of Obstetrics and Gynaecology, Leiden University Medical Centre, Leiden, The Netherlands.
authors.forename: K W M
authors.initials: KW
authors.lastname: Bloemenkamp
authors.affiliation: Department of Obstetrics and Gynaecology, Erasmus Medical Centre, Rotterdam, The Netherlands.
authors.forename: J J
authors.initials: JJ
authors.lastname: Duvekot
authors.affiliation: Department of Obstetrics and Gynaecology, Isala Clinics, Zwolle, The Netherlands.
authors.forename: B
authors.initials: B
authors.lastname: Nij Bijvank
authors.affiliation: Department of Obstetrics and Gynaecology, University Medical Centre Groningen, Groningen, The Netherlands.
authors.forename: M T M
authors.initials: MT
authors.lastname: Franssen
authors.affiliation: Department of Obstetrics and Gynaecology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: M A
authors.initials: MA
authors.lastname: Oudijk
authors.affiliation: Department of Obstetrics and Gynaecology, Maastricht University Medical Center, Maastricht, The Netherlands.
authors.forename: H C J
authors.initials: HC
authors.lastname: Scheepers
authors.affiliation: Department of Obstetrics and Gynaecology, ZGT, Almelo, The Netherlands.
authors.forename: J M
authors.initials: JM
authors.lastname: Sikkema
authors.affiliation: Department of Obstetrics and Gynaecology, Radboud University Nijmegen, Nijmegen, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: Woiski
authors.affiliation: The Robinson Institute, School of Paediatrics and Reproductive Health, University of Adelaide, Adelaide, Australia.
authors.forename: B W J
authors.initials: BW
authors.lastname: Mol
authors.affiliation: Department of Obstetrics and Gynaecology, Onze Lieve Vrouwe Gasthuis, Amsterdam, The Netherlands.
authors.forename: D J
authors.initials: DJ
authors.lastname: Bekedam
authors.affiliation: Department of Clinical Epidemiology, Biostatistics and Bioinformatics, Academic Medical Centre, Amsterdam, The Netherlands.
authors.forename: P M
authors.initials: PM
authors.lastname: Bossuyt
authors.affiliation: Department of Obstetrics and Gynaecology, Academic Medical Centre, Amsterdam, The Netherlands.|Department of Public Health, Academic Medical Centre, Amsterdam, The Netherlands.
authors.forename: M H
authors.initials: MH
authors.lastname: Zafarmand
mesh_terms: D000328:Adult; D054791:Cervical Length Measurement; D002584:Cervix Uteri; D003657:Decision Making; D005260:Female; D006801:Humans; D015999:Multivariate Analysis; D009426:Netherlands; D010570:Pessaries; D011247:Pregnancy; D011272:Pregnancy, Multiple; D047928:Premature Birth / Q000000981:diagnostic imaging / Q000517:prevention & control*; D011295:Prenatal Care; D015203:Reproducibility of Results
keywords: comparative effectiveness research; multiple pregnancies; pessary; preterm birth; treatment selection variable