Vaginal Birth After C-Section

From the SOGC’s Guidelines for Vaginal Birth After Previous Ceasarean Birth, February 2005

The rate of Ceasarean sectioned births in Canada is around 20%, most commonly for reasons of previous Ceasarean section, failure to progress, malpresentation and fetal distress.

The concern regarding VBACs involves the scar on the uterus which is an area of weakness and the resultant increased risk of uterine rupture

  • The most common presentation of a rupture is fetal distress.  Other signs may be arrest of contractions, loss of fetal presenting part on examination, abdominal pain, vaginal bleeding, hematuria and maternal cardiovascular instability.
  • Following transverse lower uterine segment incisions, the incidence of rupture is 0.2-1.5%. 
  • Following vertical lower uterine segment incisions, the incidence of rupture is 1-1.6%. 
  • Classic or “T” incisions are associated with a high rate of rupture (4-9%). 
  • The rate of uterine rupture is not increased by the use of augmentation (oxytocin). 
  • The rate is affected by the use of induction agents.  Oxytocin induction may increase the rate and should be used carefully.  Prostaglandin E2 and E1 are known to increase the rate and should not be used for induction.  It is safe to use a foley catheter to ripen the cervix.
  • Increased risk of rupture if previous C-section has been within 18-24 months

Success rates of a VBAC (1 previous C-section) is 50-85%.

Multiple previous C-sections

  • Success rate 62-89%
  • Uterine rupture rate up to 3.7%

Diabetes

  • Success rate ~64% (lower than cohort without GDM)
  • Comparable morbidities

Macrosomia

  • Lower success rates
  • No increase in morbidity/mortality, no increase in uterine rupture

Postdatism

  • Success rates are comparable
  • No significant increase in uterine rupture rates

Multiple gestations

  • Success rate 69-84%
  • No increase in materal/fetal mobidity and mortality

Medical contraindications to a VBAC include

  • Previous classic or inverted “T” uterine scar
  • Previous hysterotomy or myomectomy entering the uterine cavity
  • Previous uterine rupture
  • Contraindications to labour (malpresentation, placenta previa)

Women without medical contraindication to a VBAC should be offered a trial of labour (informed consent must be obtained) but can decline it in favour of an elective repeat C-section.

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