At first glance, the issue of vaginal birth after cesarean delivery (VBAC) appears to boil down to a simple question: Should I attempt it, or shouldn’t I?
On deeper inspection, the decision becomes extremely complex, and the evidence can be confusing.
Both planned elective repeat cesarean and planned VBAC are associated with harms as well as benefits. Most experts would agree than an uncomplicated vaginal delivery poses little risk to mother and baby, and that a planned repeat cesarean delivery at term carries some risk to the mother.
The greatest risks for both mother and baby arise when a trial of labor fails and cesarean delivery becomes necessary for maternal or fetal indications. Risks to the mother are largely operative in nature, and the primary risk to the fetus is uterine rupture. However, maternal and fetal risks cannot be truly separated. Uterine rupture not only compromises the fetus in utero but has a severe impact on maternal hemodynamic stability, just as a fetal hypoxic ischemic insult secondary to uterine rupture can have lifelong psychological and social consequences for the mother and family.
We are fortunate that serious adverse outcomes of VBAC are rare. Nevertheless, the only predictable delivery method is planned elective repeat cesarean. Uncertainty over the likelihood of success of VBAC arises when relative risk is confused with absolute risk.
In this article, I examine the literature on the route of delivery after cesarean to assess the overall safety of a trial of labor in various settings and populations.
Data on VBAC are limited
We lack randomized, controlled trials and valid animal studies that assess fetal and maternal outcomes of elective repeat cesarean versus planned vaginal delivery. The vast majority of studies of VBAC are retrospective or cohort studies, which have inherent potential for bias. Many studies lack a standardized definition of adverse outcomes or lack direct evidence that adverse outcomes are wholly attributable to the trial of labor. No studies compare women who are similar in all characteristics except their mode of delivery.
Nor do we fully understand how women choose a course of action after cesarean delivery—except that the decision is almost always multifactorial. Competing voices—health care provider, family members, friends, media, and a woman’s own memory of her previous delivery—and her emotional state—all contribute to the decision.
HOW TO APPLY THE DATA TO PRACTICE
Clearly, a trial of labor after cesarean delivery can be safe for many women. Successful vaginal delivery is associated with a very low risk of adverse outcomes and may be associated with a lower risk of minor morbidity than is elective repeat cesarean. In fact, the overall success rate for a trial of labor after cesarean is not that different from the success rate for nulliparous women undergoing induction of labor.19 Even so, patients should understand that operative delivery may be necessary, and the physician and hospital must be prepared for this eventuality in accordance with ACOG guidelines.
As I interpret the data, if a woman has undergone one low transverse cesarean delivery for a nonrecurring condition and a nonmacrosomic fetus, a trial of labor after the spontaneous onset of labor should be strongly encouraged. If she has already delivered vaginally in the past, or had a successful VBAC, she is an even better candidate for a trial of labor. In such a case, labor induction with mechanical cervical ripening or appropriate use of oxytocin, or both, may still be appropriate, but the likelihood of success is lower.
If a woman has a history of more than one cesarean delivery without a vaginal birth, she may be better served by scheduled repeat cesarean delivery. The same holds true for women who have a history of preterm cesarean delivery, a short interpregnancy interval, suspected macrosomia, or an unengaged fetal vertex.
Decision-making about delivery should be shared between the provider and patient, after thorough counseling about the risks and benefits in language the patient can easily comprehend.
It would be best to avoid having to make a decision about VBAC by preventing the initial cesarean delivery.
How risky is repeat cesarean?
We are all acutely aware of the skyrocketing rate of cesarean delivery, which reaches 35% to 41% in some areas. Most studies indicate that approximately 50% of all cesarean deliveries are repeat cesarean deliveries. Besides the risks associated with the operation itself, planned repeat cesarean has significant downstream implications for the mother and baby—and for society. For example, multiple cesarean deliveries pose an ever greater risk of abnormal placentation and maternal hemorrhage. Cesarean delivery without labor can also heighten the risk of neonatal respiratory compromise, temperature instability, and slow feeding.1 Cesarean delivery and its longer attendant hospitalization markedly increase costs throughout an already strapped health care system.