It is standard practice for doctors to
use a low, side-to-side (transverse) incision across the uterus for a
cesarean delivery. But a vertical type of
incision is sometimes needed, such as for some emergency cesarean
Before deciding whether you are a good candidate for a safe
vaginal birth after cesarean (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
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
Is unlikely to rupture during a subsequent labor and
Has been increasingly used for cesarean 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 labor.
Is more likely to break open
(rupture) during a subsequent labor, particularly if the incision is high
rather than low on the uterus. This risk applies to all uterine scars that are
not low transverse.
Is very rarely used for cesarean
Uterine rupture rates
Women who have a low transverse cesarean
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 labor.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 cesarean 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
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 labor.2
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.
Cunningham FG, et al. (2010). Prior cesarean
delivery. In Williams Obstetrics, 23rd ed., pp. 565–576.
New York: McGraw-Hill.
How this information was developed to help you make better health decisions.