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2.1.2 Success Rates of ECV and Predictive Factors

Success Rates of ECV

Conclusion: Average success rate approximately 49-58% with lower rates in nulliparous women.​

2008 Meta-analysis in Obstetrics & Gynecology looking at 84 studies​:

  • Successful version rates ranged from 16-100% ​
  • Overall pooled success rate was 58% 

2019 large cohort study in BJOG with 2614 women undergoing ECV​

  • Overall success 49%, 95% CI 47.0-50.9%​
  • 40% nulliparous women​
  • 64% in others ​
  • 97.3% cephalic at birth​

Positive Predictive Factors​

Summary of Positive Predictive Factors of ECV Success:

  • Parity​
  • Ultrasound measured size of amniotic fluid preceding the fetal part (fore-bag) ​
  • Transverse or oblique lie​


  • Single-centre retrospective study including all candidates for ECV between 36-41 weeks GA​
  • Variables: BMI, AFI, GA, parity, location of placenta, fetal trunk posture, time in breech presentation before the procedure, and ultrasound measured size of amniotic fluid preceding the fetal part (fore-bag) ​


  • Patients with BMI >29 had lower probability of success regardless of fore-bag size​
  • Version outcome in BMI <29 was associated with fore-bag size ​
  • Fore-bag size >1 cm had higher success rate​
  • Fore-bag size <1cm in nulliparous women resulted in lower success than multiparous women ​
  • One-unit increase in BMI resulted in reduced odds of success (OR 0.6) 
  • Number of previous deliveries increased odds (OR 6)

Negative Predictive Factors

  • Nulliparity​
  • Advanced dilation​
  • Fetal weight <2500 g​
  • Anterior placenta​
  • Low station/descent of breech into pelvis​

Controversial Factors​

  • Normal or increased amniotic fluid volume​
  • Location of placenta​
  • Maternal weight ​
  • Early labour ​

Impact of Provider Experience on Success

Introduction of a dedicated team increases the success rate of external cephalic version: A prospective cohort study (Thissen et.al., 2019)

  • Prospective cohort study, N=673 women with singleton breech fetus comparing ECV success rate prior to and after a dedicated team​
  • Dedicated team of 6 gynecologists and 6 midwives ​
  • Standard information for patients (leaflet, movie, ECV checklist with informed consent and risks)​
  • Absolute contraindications: mutiples, labour, indication for planned C/S, abnormal umbilical Dopplers, Rh immunization, vaginal bleeding <7 days prior, placental previa, ruptured membranes, suboptimal FHR, congenital uterine abnormalities​


  • ECV Success rate increased from 39.8% to 69.5% (p<0.001)​
  • Greatest increase was seen in nulliparous women from 23.5% to 58.5%, P=0.002​
  • Found an increase in vaginal delivery rate and decrease in c-section rate ​


ECV performance by a dedicated team, consisting of experienced providers increases ECV success rate. ​

Impact of Timing of ECV on Success – Is Earlier Better?

Unblinded multi-centre RCT ​

N=1534 with singleton breech fetus​

Randomized to:

1) Early ECV at 34+0 to 35+6 weeks GA (n=767)​

2) Delayed ECV at >37+0 weeks GA (n=774)​

Primary outcome: rate of c-section ​

Secondary outcome: rate of preterm birth ​


Early ECV resulted in fewer fetuses in non-cephalic presentation (RR 0.84, 95% CI 0.75-0.94) with no difference in rates of c-section (52% vs 56%, RR 0.93, CI 0.85-1.05) or risk of preterm birth (6.5% vs 4.4%, RR 1.48, 95% CI 0.97-2.26) 


​Early ECV increases the likelihood of cephalic presentation at birth with no decrease in c-section rate or increase in preterm birth risk.​

Impact of BMI on Rates of Successful ECV in Those with Prior Cesarean Section

  • Cross-sectional study looking at 2329 women who underwent ECV after one previous c-section​.


  • No correlation of BMI with the rate of successful ECV along women with one prior c- section. ​
  • Risks of adverse maternal and neonatal outcomes were similar. 

Impact of Persistent Breech Presentation on Rates of Successful ECV

  • Persistent breech presentation defined as persistent breech presentation during all ultrasound examinations performed between the anatomy scan and the gestational week when ECV was attempted​
  • N=684 women underwent ECV attempt​
  • Overall success rate of 61.5% ​
  • Persistent breech success rate: 19.6%​
  • Not persistent breech success rate: 82.0%​
Updated on June 28, 2021

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