that these new, less restrictive guidelines are in place, mothers-to-be
facing decisions about vaginal birth after cesarean section (VBAC) need
to keep two important numbers in mind.
The first is their likelihood of having a successful VBAC, which is generally quoted as 60-70 percent. That proportion goes up if the woman has had a previous vaginal birth or if her previous abdominal delivery was for a reason that is unlikely to repeat itself, such as a breech delivery. The number declines if labor is induced rather than allowing a natural progression or as her baby’s size increases.
The second important number is the likelihood of the uterine scar coming open prior to delivery, which generally happens less than 1 percent of the time. Some of these ruptured wounds will be minor and of little consequence, but some are obstetrical emergencies that endanger the life and long term health of the baby. Scar rupture risk increases when labor is induced or stimulated (with medicines to speed labor up) and also increases as the baby increases in size. We are poor estimators of fetal weight, even with ultrasound, so the clinical usefulness of baby size estimates are of little practical help to clinicians or mother.
Thus, the woman making a decision about VBAC must keep these two probabilities in mind. Ultimately, final decisions turn on how the individual values natural childbirth and her fear, or lack thereof, about surgery.
Women attempting VBAC should do so in a hospital that can respond in a timely fashion to the rare but serious risk of scar rupture.