Doctors used to insist “once a C-section, always a C-section.” Today it is standard practice to allow vaginal births after C-section (VBAC) for appropriately selected patients. The American Congress of Obstetricians and Gynecologists (ACOG) has issued a Practice Bulletin to guide obstetricians in determining which patients are appropriate candidates for VBAC.
We frequently hear criticisms of practice guidelines like these. The doctors who write the guidelines are accused of conflict of interest, turf protection, and biased evaluation of the evidence. For those who believe doctors put profits before patients, this should be an eye-opener. It would presumably be in the best financial interests of obstetricians to do as many C-sections as possible, since they can charge more for them than for vaginal births. It would have been easy for the ACOG to put a spin on the data to make repeat C-sections look like a better choice. The fact that they offer VBACs despite their conflict of interest makes me think that their evaluation of the evidence was probably fair and unbiased.
So just how safe is VBAC? What are the pros and cons? What does the evidence say?
Background: Why is VBAC an issue?
The earlier prohibition of vaginal deliveries after C-sections was due to the risk of uterine rupture and other complications. In the 1970s, doctors began to reconsider. The percentage of women with a VBAC rose from 5% in 1985 to 28% in 1996; but then the number of reports of uterine rupture began to increase, and by 2006 the VBAC rate had dropped to 8.5%. Between 2003 and 2006, 26% of obstetricians stopped offering it. An NIH panel examined the evidence in 2010. They concluded that VBAC was a reasonable option and called on the ACOG and other organizations to facilitate access to it.
Trial of labor doesn’t always succeed
There are three possible outcomes for a trial of labor: a successful vaginal birth, an emergency C-section, or an elective C-section. Only 74% of women who attempt VBAC succeed; the other 26% ends up needing a C-section, often on an emergency basis. Emergency surgeries are inherently more risky than planned ones. A number of factors have been identified that affect the chance of a successful vaginal delivery, including race, maternal age, fetal size, fetal position, gestational age, mother’s weight, number of previous C-sections, a previous vaginal birth, the reason the C-section was done, cervical effacement and dilation at the time of admission, rupture of membranes, induction of labor, and the presence of meconium. Screening tools have been developed to help predict outcomes. The models make good predictions at the population level, but they haven’t been verified as useful for individual women.
Benefits and harms to mothers with VBAC
The NIH panel graded the available evidence. They found:
- High-grade evidence for a lower death rate for women attempting VBAC: 4 per 100,000 compared to 13 per 100,000 with elective repeat C-section
- Moderate-grade evidence for increased risk of uterine rupture. 778 per 100,000 compared to 22 per 100,000 for elective repeat C-section:
- No maternal deaths from uterine rupture
- 6% of ruptures are fatal for the infant
- 14-33% of ruptures require hysterectomy
- A number of factors are known to increase the risk of rupture, including induction of labor and the number of previous C-sections
- A prior vaginal birth reduces the risk of rupture to 600 per 100,000
- Moderate-grade evidence for a lower risk of placental abnormalities like placenta previa in future pregnancies
- Low-grade evidence for a shorter hospital stay and a lower rate of deep venous thrombosis with VBAC
Harms and benefits of VBAC for infants
The NIH found:
- Moderate-grade evidence that perinatal mortality is increased: 130 per 100,000 compared to 50 per 100,000 for elective repeat C-section
- Low-grade evidence for higher fetal mortality in utero (50-100 per 100,000 versus 0-40 per 100,000)
- Low-grade evidence for a higher rate of hypoxic ischemic encephalopathy
- Insufficient evidence for a difference in respiratory problems, sepsis, birth trauma, breastfeeding practices or mother-infant bonding
Nonmedical factors that influence utilization of VBAC
- Professional guidelines require that VBAC be offered only where emergency C-sections are “immediately available.” 30% of hospitals stopped offering VBAC because they couldn’t guarantee immediate surgical and anesthesia services. Oregon midwives are upset because the Oregon Health Plan excluded VBACs from coverage for non-hospital births. Midwives are still attempting VBACs in home births, and some have called VBAC a “success” even when the baby died. At least the mother had a “natural” experience and avoided surgery!
- Professional liability concerns. There have been lawsuits: a patient whose doctor informed her about the risk of uterine rupture sued because she claimed she was not specifically told there was a possibility that the baby could die
- Informed decision-making is problematic due to insufficient data and the impact of how the risk is presented to the patient
- High volume settings tend to have better outcomes
- Patient and provider preferences: considerations like the belief that vaginal delivery is deeply empowering, the expectation of an easier recovery, a desire for sterilization at the time of delivery, the desire to avoid labor pain, the expense, a previous bad experience, etc.
Conclusions of the NIH
The NIH panel concluded that a trial of labor is a reasonable option for many pregnant women with one prior C-section with a low transverse uterine incision. The reduced risk for the mother and the increased risk for the infant pose a profound ethical dilemma that is made worse by the paucity of high-quality evidence and the difficulty of providing precise quantification of the risks and benefits for informed consent.
The American Congress of Obstetricians and Gynecologists Practice Bulletin (as of 2015) essentially agrees with the findings of the NIH group. It reviews the evidence for risk and benefit and provides practical guidelines for managing and counseling patients who will give birth after a previous C-section.
They point out that there are no randomized controlled trials, and that the available evidence is from observational studies. They remind us that the appropriate comparison is not between VBAC and surgery, but between trial of labor after C-section (TOLAC) and elective repeat C-section, since many of the attempts end in a C-section anyway and most of the morbidity from TOLAC occurs when a repeat C-section becomes necessary.
VBAC is associated with fewer complications, and a failed TOLAC is associated with more complications, than elective repeat cesarean delivery. Consequently, risk for maternal morbidity is integrally related to a woman’s probability of achieving VBAC.
They point out that some studies have lumped together catastrophic uterine ruptures and asymptomatic scar dehiscences. They estimate the risk of rupture as 0.5-0.9% after TOLAC. After a woman has had a uterine rupture, the risk of a repeat rupture is 6%; they recommend early delivery by C-section for those patients.
Women who achieve VBAC avoid major surgery with its inherent risks and its consequences for the success of future pregnancies (like abnormal placentation). They have lower rates of hemorrhage, infection, and a shorter recovery period.
They stress that the probability of a successful VBAC depends on a combination of factors. They list those factors and they mention a model that may be helpful in quantifying predictions. They cover a lot of special situations like twin gestations and intrauterine demise. As with so much else in medicine, it’s complicated. Counseling should involve consideration of all the relevant individual factors that might increase or decrease risk beyond the average, and the ultimate decision should be made by the woman.
They point out that there should be “immediately available” emergency resources, which may preclude offering VBAC in smaller facilities.
They offer detailed recommendations and specify which recommendations are based on which levels of evidence: A (good and consistent scientific evidence), B (based on limited or inconsistent scientific evidence) or C (primarily based on consensus and expert opinion). They propose a performance measure: the percentage of women who are candidates for TOLAC for whom discussion of the risks and benefits of TOLAC compared with a repeat C-section are documented in the medical record.
Conclusion: Easier for moms, harder on babies
How safe is VBAC? The evidence is not as extensive or as high-quality as we would wish, so there are no definitive answers. But based on the evidence we do have, VBAC appears to be a trade-off, with a small decrease in risk for mothers and a small increased risk for babies. Those risks vary according to a lot of different factors, and patients should be counseled by obstetricians who can use their clinical judgment to estimate how the individual’s risk factors might affect the interpretation of the overall statistics. The Skeptical OB has described how this individualized approach works. There are non-medical factors to consider, and ultimately the woman has to decide what risks she is willing to accept for herself and her child.