The National Institutes of Health released a comprehensive review of outcomes of vaginal birth after cesearean (VBAC). They study, entitled Vaginal birth after cesarean: new insights by Guise et al. is a comprehensive review of the literature.
In analyzing maternal and perinatal mortality, The authors found:
Overall rates of maternal harms were low for both TOL and ERCD. While rare for both TOL and ERCD, maternal mortality was significantly increased for ERCD at 13.4 per 100,000 versus 3.8 per 100,000 for TOL. The rates of maternal hysterectomy, hemorrhage, and transfusions did not differ significantly between TOL and ERCD. The rate of uterine rupture for all women with prior cesarean is 3 per 1,000 and the risk was significantly increased with TOL (4.7/1,000 versus 0.3/1,000 ERCD). Six percent of uterine ruptures were associated with perinatal death… Perinatal mortality was significantly increased for TOL at 1.3 per 1,000 versus 0.5 per 1,000 for ERCD.
In other words, elective repeat cesarean delivery (ERCD) increases the rate of maternal death compared to trial of labor (TOL) by approximately 9/100,000. However, TOL increases the risk of perinatal death by 80/100,000.
Let’s look at the findings in detail.
Maternal death
Overall, the strength of evidence regarding the rate of mortality for women with a prior cesarean delivery is high with good consistency and precision. While maternal mortality is rare .., the risk of maternal mortality is significantly increased with ERCD. When combining the TOL group across all studies, the risk of maternal mortality is found to be 0.0038 percent (95 percent CI: 0.0009 to 0.0155 percent). The combined risk for ERCD group across all studies is 0.0134 percent (95 percent CI: 0.0043 to 0.0416 percent). This translates to 3.8 per 100,000 for TOL (95 percent CI: 0.9 to 15.5 per 100,000) and 13.4 per 100,000 for ERCD (95 percent CI: 4.3 to 41.6 per 100,000)…
While rare for both TOL and ERCD, compared to ERCD, the overall risk of maternal death associated with TOL is significantly lower (RR, 0.33, 95 percent CI: 0.13 to 0.88; p=0.027). Using 0.0134 percent as the baseline risk for ERCD, the calculated risk difference is −0.0090 percent (95 percent CI: −0.0117 to 0.0016 percent), translating to 9.0 less deaths per 100,000 (95 percent CI: 1.6 to 11.7 less deaths per 10,000) from the TOL group…
Uterine rupture
… Among these four studies totaling 47,202 patients, there were 154 uterine ruptures; 96 percent (N=148) of which were incurred by the TOL group… Within these four studies, the combined risk of uterine rupture for women undergoing a TOL is 0.47 percent (95 percent CI: 0.28 to 0.77 percent) and 0.026 percent (95 percent CI: 0.009 to 0.082 percent) for women undergoing an ERCD…
… [T]he occurrence of uterine rupture for TOL remains relatively unchanged at 0.46 percent. Among TOL studies, the occurrence of uterine rupture is significantly higher for studies limited to term patients compared with studies including patients of any GA (0.78 versus 0.32 percent, p=0.033)…There were no uterine ruptures among women who experienced ERCD without labor for any direction of incision…
Morbidity and mortality of rupture
… [T]here were no maternal deaths due to uterine rupture in any of the eight studies. The risk for perinatal death in the event of uterine rupture ranged from 0 to 20 percent with a pooled risk of 6.2 percent and the highest risk experienced by the TOL group…
Overall, evidence regarding the rate of uterine rupture for women with a prior cesarean delivery is moderate in strength … Compared with women undergoing an ERCD, women undergoing a TOL have a significantly higher risk of uterine rupture (RR 20.74, 95 percent CI: 9.77 to 44.02; p<0.0010)... To date, there have been no maternal deaths reported because of uterine rupture, and the risk of perinatal death due to uterine rupture is similarly low at 6.2 percent. However, the risk of hysterectomy due to uterine rupture is an important consideration for women planning VBAC, with rates ranging from 14 to 33 percent...
Perinatal death
… The risk of perinatal mortality was significantly higher for TOL as compared with ERCD (RR 1.82; 95 percent CI: 1.24 to 2.67; p=0.041). Using 0.05 percent as the baseline risk for ERCD, the calculated risk difference was 0.41 percent (95 percent CI: 0.012 to 0.08 percent) which is equivalent to .41 more deaths among women who attempt TOL…
Neonatal death
… The risk of neonatal mortality was significantly higher for TOL compared with ERCD with a calculated risk difference of 0.058 percent (95 percent CI 0.019 to 0.117 percent), which is equivalent to .58 additional perinatal deaths per 1,000 for TOL.
Subsequent babies
Two studies were reviewed to determine the risk of stillbirth in subsequent pregnancies in women with a prior cesarean delivery. These studies produced conflicting results with one study showing that prior cesarean increases the risk for unexplained stillbirth in next pregnancy and the other study showing no difference in risk for stillbirth in the next pregnancy…
The authors summarize their findings:
One of the major findings of this report is that the best evidence suggests that VBAC is a reasonable and safe choice for the majority of women with prior cesarean. The occurrence of maternal and infant mortality for women with prior cesarean is not significantly elevated when compared with national rates overall of mortality in childbirth. The majority of women who have TOL will have a VBAC, and they and their infants will be healthy. However, there is a minority of women who will suffer serious adverse consequences of both TOL and ERCD…
What are we to make of these findings?
The absolute level of risk for both TOL and ERCD is low. ERCD is associated with a risk of maternal death of 9/100,000. Although the cesareans are classified as “elective.” that does not mean that the women who chose them were good candidates for VBAC, so it is not clear how many of these C-sections were truly elective. TOL is associated with a perinatal death rate of 80/100,000. Although there is a decreased risk of maternal death, there is a dramatically increase rate of uterine rupture rate of 460/100,000. Since many of those women (14-33%, or 64-153/100,000) will go on to have a hysterectomy due to the rupture, TOL increases the risk of serious maternal morbidity.
This literature review essentially confirms what we already knew. VBAC increases the rate of perinatal death, uterine rupture and subsequent hysterectomy, while ERCS has a higher rate of maternal death. albeit an order of magnitude smaller than the VBAC associated increased risk of perinatal death.
