VBAC: Type of Past Incision

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VBAC: Type of Past Incision

Topic Overview

It is standard practice for doctors to use a low, side-to-side (transverse) incision across the uterus for a caesarean delivery. But a vertical type of incision is sometimes needed, such as for some emergency caesarean deliveries.

Before deciding whether you are a good candidate for a safe vaginal birth after caesarean (VBAC), you and your doctor must first confirm what kind of uterine incision you have had. Because the outward scar is not always positioned over the uterine scar, checking your medical record is the only dependable way to be sure of your incision type.

A low transverse (horizontal) incision:

  • Cuts across the lower, thinner part of the uterus. These muscles don't contract as strongly as the upper uterus during labour.
  • Is unlikely to rupture during a subsequent labour and delivery.
  • Has been increasingly used for caesarean deliveries since the 1970s and is the usual practice among obstetricians.

A vertical (classical) incision:

  • Cuts up and down through the uterine muscles that strongly contract during labour.
  • Is more likely to break open (rupture) during a subsequent labour, particularly if the incision is high rather than low in the uterus. This risk applies to all uterine scars that are not low transverse.
  • Is very rarely used for caesarean deliveries.

Uterine rupture rates

Women who have a low transverse caesarean scar have a lower risk of rupturing than women who have a vertical incision. About 5 to 9 out of 1,000 women (0.5% to 0.9%) with a low transverse scar have a uterine rupture during a trial of labour.1 (It is likely that the women who rupture have other risk factors that make them more vulnerable to this complication.)

Women who have a low vertical caesarean scar (which is only on the lower uterus) are as likely to deliver vaginally as they would be with a low transverse scar. And they have no higher risk of complications, including rupture.1 Some doctors are willing to allow a woman with a very low vertical incision to try VBAC, but most doctors are not. This is because of the concern about uterine rupture.

A woman with a vertical (classical) incision has the greatest uterine rupture risk. About 40 to 90 out of 1,000 women (4% to 9%) with this type of vertical incision scar have a uterine rupture during a trial of labour.2



  1. American College of Obstetricians and Gynecologists (2010). Vaginal birth after previous cesarean delivery. ACOG Practice Bulletin No. 115. Obstetrics and Gynecology, 116(2): 450–463.
  2. Cunningham FG, et al. (2010). Prior cesarean delivery. In Williams Obstetrics, 23rd ed., pp. 565–576. New York: McGraw-Hill.


By Healthwise Staff
Primary Medical Reviewer Sarah Marshall, MD - Family Medicine
Primary Medical Reviewer Anne C. Poinier, MD - Internal Medicine
Specialist Medical Reviewer Femi Olatunbosun, MB, FRCSC - Obstetrics and Gynecology
Last Revised May 31, 2011

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