title: Transvaginal cervical length scans to prevent prematurity in twins: a randomized controlled trial.
abstract: BACKGROUND
  Twin pregnancies are associated with an increased risk of perinatal morbidity and mortality primarily due to spontaneous preterm deliveries. The mean gestational age for delivery is 35.3 weeks and twins account for 23% of preterm births <32 weeks. A number of strategies have been proposed to prevent preterm deliveries: tocolytics, bed rest, hospitalization, home uterine activity monitoring, cerclage, and most recently, progesterone. Unfortunately, none have proven effective. Recent metaanalyses and reviews suggest that transvaginal cervical length (TVCL) ultrasound in the second trimester is a powerful predictor of preterm birth among asymptomatic women. Indeed, TVCL has the highest positive and negative predictive values for determining the risk of spontaneous preterm delivery in twin pregnancies. It follows that TVCL assessment may allow identification of a subset of twin pregnancies that re better candidates for interventions intended to prevent prematurity.
  
  
  OBJECTIVE
  We sought to determine whether use of TVCL prolongs gestation in twin pregnancies.
  
  
  METHODS
  This is a multicenter, randomized, controlled trial of 125 dichorionic or monochorionic/diamniotic twin pregnancies without prior preterm birth <28 weeks. The study group (n = 63) had TVCL and digital exams monthly from 16-28 weeks and were managed with a standard algorithm for activity restriction and cerclage. The control group (n = 62) had monthly digital cervical examinations but no routine TVCL ultrasound examinations. The primary outcome was gestational age at delivery. Secondary outcomes included percentage of deliveries <35 weeks, and maternal and neonatal outcomes.
  
  
  RESULTS
  The mean gestational age at delivery was 35.7 weeks (95% confidence interval [CI], 35.2-36.2) among those managed with TVCL and 35.5 weeks (95% CI, 34.7-36.4) among the control patients. The Kaplan-Meier estimates of deliveries <38 weeks were not significantly different between groups. This was true whether we compared curves with a log-rank test (P = .67), Breslow test (P = .67), or Tarone-Ware test (P = .64). The percentage of deliveries <35 0/7 weeks did not differ: 27.4% for subjects managed with routine TVCL and 28.6% for control subjects (relative risk, 0.96; 95% CI, 0.60-1.54). Our study had an 80% power to detect a 12-day difference in the gestational age at delivery with 95% confidence.
  
  
  CONCLUSIONS
  The overall mean length of gestation and the percentage of women delivering <35 weeks did not differ between twin gestations managed with TVCL and digital exams monthly from 16-28 weeks with a standard algorithm for activity restriction and cerclage and controls who had monthly digital cervical examinations but no routine TVCL. Routine second-trimester transvaginal ultrasound assessment of cervical length is not associated with improved outcomes when incorporated into the standard management of otherwise low-risk twin pregnancies.
authors.affiliation: Department of Obstetrics and Gynecology, Wilford Hall Medical Center, Lackland Air Force Base, TX. Electronic address: packergord@aol.com.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Gordon
authors.affiliation: Department of Obstetrics and Gynecology, Wright-Patterson Medical Center, Wright-Patterson Air Force Base, OH; Wright State University, Dayton, OH.
authors.forename: David S
authors.initials: DS
authors.lastname: McKenna
authors.affiliation: Department of Obstetrics and Gynecology, Wilford Hall Medical Center, Lackland Air Force Base, TX.
authors.forename: Theresa L
authors.initials: TL
authors.lastname: Stewart
authors.affiliation: Department of Obstetrics and Gynecology, Madigan Army Medical Center, Tacoma, WA; Department of Obstetrics and Gynecology, University of Tennessee Medical Center, Knoxville, TN.
authors.forename: Bobby C
authors.initials: BC
authors.lastname: Howard
authors.affiliation: Department of Obstetrics and Gynecology, Wright-Patterson Medical Center, Wright-Patterson Air Force Base, OH.
authors.forename: Kimberly F
authors.initials: KF
authors.lastname: Foster
authors.affiliation: Center for Maternal-Fetal Care, San Antonio, TX.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Higby
authors.affiliation: Department of Obstetrics and Gynecology, Wilford Hall Medical Center, Lackland Air Force Base, TX.
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: Cypher
authors.affiliation: Department of Obstetrics and Gynecology, Wilford Hall Medical Center, Lackland Air Force Base, TX; Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA.
authors.forename: William H
authors.initials: WH
authors.lastname: Barth
mesh_terms: D000328:Adult; D001510:Bed Rest / Q000379:methods*; D023802:Cerclage, Cervical / Q000379:methods*; D054791:Cervical Length Measurement; D002584:Cervix Uteri / Q000000981:diagnostic imaging*; D036861:Delivery, Obstetric; D005260:Female; D006801:Humans; D053208:Kaplan-Meier Estimate; D011247:Pregnancy; D059285:Pregnancy, Twin; D047928:Premature Birth / Q000517:prevention & control*; D018570:Risk Assessment; D055815:Young Adult
keywords: prematurity prevention; transvaginal cervical length; twins