title: Prediction of preterm delivery in twin pregnancy: a prospective, observational study of cervical length and fetal fibronectin testing.
abstract: OBJECTIVE
  To evaluate prospectively cervical length measurements and fetal fibronectin detection as predictors of spontaneous preterm delivery in an unselected population of twin pregnancies.
  
  
  METHODS
  Transvaginal ultrasound assessments of cervical length were performed serially at 18, 24, 28 and 32 weeks' gestation. Receiver-operating characteristic curves were generated at each time point to determine the optimal cut-off for cervical length and rate of change in cervical length in the prediction of preterm delivery (< 35 weeks). A bedside assay for the detection of fetal fibronectin in the maternal vaginal secretions was performed prior to cervical length measurements from 24 weeks. Likelihood ratios (LRs) were used to assess the performance of each test.
  
  
  RESULTS
  The spontaneous preterm delivery rate was 16.5% in 91 studied twin pregnancies. A cervical length </= 25 mm at 18 weeks (LR+ 9.7, sensitivity 14.3%) and </= 22 mm at 24 weeks (LR+ 9.6, sensitivity 28.6%) were the best predictors of preterm delivery. A shortening of cervical length >/= 2.5 mm per week between 18 and 28 weeks' gestation also predicted preterm delivery (LR+ 10.8, sensitivity 16.7%). There was no relationship between the detection of fetal fibronectin and preterm delivery.
  
  
  CONCLUSIONS
  This study confirms the value of transvaginal ultrasound assessment of cervical length as a predictor of preterm delivery in twin pregnancies. However, the poor sensitivity of this test makes it unsuitable as a single predictor of preterm delivery. Fetal fibronectin testing does not identify twin pregnancies destined to deliver prematurely.
authors.affiliation: The Queen Mother's Hospital, Glasgow, UK. janicelgibson@hotmail.com
authors.forename: J L
authors.initials: JL
authors.lastname: Gibson
authors.forename: L M
authors.initials: LM
authors.lastname: Macara
authors.forename: P
authors.initials: P
authors.lastname: Owen
authors.forename: D
authors.initials: D
authors.lastname: Young
authors.forename: J
authors.initials: J
authors.lastname: Macauley
authors.forename: F
authors.initials: F
authors.lastname: Mackenzie
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D002584:Cervix Uteri / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000473:pathology; D005260:Female; D005353:Fibronectins; D005865:Gestational Age; D006023:Glycoproteins / Q000032:analysis*; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D007752:Obstetric Labor, Premature / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000473:pathology; D011247:Pregnancy; D011256:Pregnancy Outcome; D011446:Prospective Studies; D012372:ROC Curve; D014427:Twins; D016216:Ultrasonography, Prenatal / Q000379:methods*
chemical_list: D015415:Biomarkers; C403421:FFN protein, human; D005353:Fibronectins; D006023:Glycoproteins