title: Cervical assessment by ultrasound for preventing preterm delivery.
abstract: BACKGROUND
  Measurement of cervical length (CL) by transvaginal ultrasound (TVU) is predictive of preterm birth (PTB). It is unclear if this screening test is effective for prevention of PTB.
  
  
  OBJECTIVE
  To assess the effectiveness of antenatal management based on TVU CL screening for preventing PTB.
  
  
  METHODS
  We searched the Cochrane Pregnancy and Child birth Group's Trials Register (September 2008), MEDLINE (1966 to September 2008), and reviewed the reference list of all articles.
  
  
  METHODS
  : Published and unpublished randomized controlled trials including pregnant women between the gestational ages of 14 to 32 weeks screened with TVU CL for risk of PTB. This review focuses exclusively on studies based on knowledge versus no knowledge of TVU CL results.
  
  
  METHODS
  All potential studies identified as in the search were assessed for inclusion by three independent review authors. We also analyzed studies for quality measures and extracted data.
  
  
  RESULTS
  Of 12 trials identified, five were eligible for inclusion (n=507). Three included singleton gestations with preterm labor (PTL); one included singleton gestations with preterm prelabour rupture of membranes (PPROM); and one included twin gestations without or with PTL.In the three trials of singleton gestations with PTL, 290 women were randomized; 147 to knowledge and 143 to no knowledge of TVU CL. Knowledge of TVU CL results was associated with a non-significant decrease in PTB at less than 37 weeks (22.3% versus 34.7%, respectively; risk ratio 0.59, 95% (CI) 0.26 to 1.32). Delivery occurred at a later gestational age in the knowledge versus no knowlege groups (mean difference 0.64 weeks (CI 0.03 to 1.25)). All other outcomes for which there were available data (PTB at less than 34 or 28 weeks; birthweight less than 2500 grams; perinatal death; maternal hospitalization; tocolysis; and steroids for fetal lung maturity) were similar in the two groups.The trial of singleton gestations with PPROM (n=92) evaluated as its primary outcome safety of TVU CL in this population, and not its effect on management. The incidence of maternal and neonatal infections was similar in the TVU CL and no TVU CL groups.In the trial of twin gestations with or without PTL (n=125), PTB at less than 36, 34, or 30 weeks, gestational age at delivery, and other perinatal and maternal outcomes were similar in the TVU CL and the no TVU CL groups. Life table analysis revealed significantly less preterm birth at less than 35 weeks in the TVU CL group compared to the no TVU CL group (P=.02).
  
  
  CONCLUSIONS
  Currently there is insufficient evidence to recommend routine screening of asymptomatic or symptomatic pregnant women with TVU CL. Since there is a non-significant association between knowledge of TVU CL results and a lower incidence of PTB at less than 37 weeks in symptomatic women, we encourage further research. Future studies should look at specific populations separately (eg singleton versus twins; symptoms of PTL or no such symptoms), report on all pertinent maternal and perinatal outcomes, and include cost-effectiveness analyses. Most importantly, future studies should include a clear protocol for management of women based on TVU CL results, so that it can be easily evaluated and replicated.