Is vaginal birth after cesarean an endangered procedure? Most women who attempt a trial of labor after cesarean have good outcomes, and those at high risk for adverse events, who should be excluded, are becoming increasingly better defined. Yet many physicians eschew this option altogether because of serious concerns about the safety of trial of labor after cesarean.1
If VBAC is to play a role in obstetrical management in the 21st century, we will need to improve our ability to distinguish these 2 populations:
- women with a low risk for complications and a high likelihood of a successful trial of labor, and
- women at high risk for adverse outcomes.
Of many reports documenting risk factors for the most feared complication, uterine rupture, none are from randomized controlled studies of trial of labor after cesarean versus elective repeat cesarean (and such reports are unlikely to be forthcoming). Therefore, we must depend on less rigorously obtained information. Nonetheless, we do have a wealth of data to guide us.
The 8 “pearls” in this article summarize what we know from the available data on vaginal birth after cesarean.
- The repeat cesarean rate varies by prior indication for cesarean: lowest for breech; highest for failure to progress.
- Induced labor has a higher rate of repeat cesarean than spontaneous labor.
- Maternal obesity and fetal macrosomia lower the success rate.
- Induction with oxytocin is associated with an increased risk of uterine rupture, but oxytocin can be used judiciously for augmentation of labor.
- Prostaglandins should not be used for cervical ripening or induction.
- Having more than 1 prior cesarean increases risk of uterine rupture.
- Interdelivery intervals of up to 18 months and maybe even 24 months are associated with an increased risk for uterine rupture. Women should be discouraged from becoming pregnant for at least 9 months, and possibly up to 15 months, after cesarean, if they are contemplating a trial of labor after cesarean for their next delivery.
- Uterine rupture is 5 times less likely in women who have had a vaginal delivery either before or after a prior cesarean delivery.
Pearl 1VBAC rate varies by prior indication
The overall rate of successful vaginal delivery for all women attempting trial of labor after cesarean varies from approximately 60% to 80%.
We showed, however, that the repeat cesarean rate varies by prior indication for cesarean. The rate for those whose prior cesarean was due to breech presentation was 13.9%, which approximated the cesarean rate among nulliparas during the study period (13.5%). The highest rate of repeat cesarean, 37.3%, was for those whose prior cesarean was for failure to progress.2
Pearl 2Repeat cesarean rate is higher with induced labor
Failed induction is a risk for all gravidas having labor induced, regardless of any prior cesarean deliveries. It is especially common among women with an unripe cervix.
Among women with a prior cesarean, labor induction has an approximately 10% increased rate of repeat cesarean, compared with those undergoing spontaneous labor.3
Pearl 3Successful VBAC rate is lower with maternal obesity or fetal macrosomia
Recent evidence suggests that both maternal and fetal weights influence the success of trial of labor after cesarean.
Maternal obesity is associated with a decreased success rate for trial of labor after prior cesarean delivery, but the magnitude of this risk is not well characterized: A success rate of 13% for morbidly obese women has been documented4; more recently, however, a success rate of 57% was reported.5 These studies are limited by their small numbers.
The factors most important for counseling a woman about obstetrical management after a prior cesarean are her likelihood of success from trial of labor, and the risks and benefits of both trial of labor and an elective repeat cesarean.
The findings noted in this article call for a scoring system that will more precisely define the risk for an individual patient contemplating trial of labor after prior cesarean.
Over the past 3 decades, multiple studies have attempted to predict the success of trial of labor after cesarean. Flamm and Geiger19 reported a 10-fold predicted difference in the rate of cesarean based on a scoring system incorporating:
- maternal age,
- prior vaginal delivery,
- prior indication for cesarean, and
- the intrapartum assessment of cervical dilation and effacement.
Others have used additional variables including:
- estimated fetal weight,
- gestational age,
- prepregnancy body mass index,
- maternal weight gain, and
- induction of labor.20-23
With further investigation and better identification of those at highest and lowest risk, we will be better able to counsel each patient on her individual risks for a uterine rupture during a trial of labor after prior cesarean delivery.