“To VBAC or not to VBAC” continues to be the question. “Mode of delivery after a previous cesarean birth, and associated maternal and neonatal morbidity,” a recent analysis of Canadian national data between 2003 and 2014, compared maternal and neonatal mortality and morbidity after planned vaginal birth after cesarean (VBAC ) versus repeat cesarean and concluded (Young 2018): “Although absolute rates of adverse outcomes are low, attempted vaginal birth after cesarean delivery continues to be associated with higher relative rates of severe morbidity and mortality in mothers and infants.” However, things aren’t always as they appear to be at first glance. Let’s take a closer look.

The investigators limited the population to women who had a first delivery by cesarean and no other births (197,540 women) and who delivered at term a singleton baby free of congenital anomalies either as a planned VBAC (58,704 women) or a planned repeat cesarean (138,836 women).

Already we have a problem. The title and conclusion don’t make clear that the investigators are only talking about second delivery after a first cesarean. This means their findings don’t apply to women who had a vaginal birth either before or after their cesarean, these women being at much lower risk for scar rupture (Gyamfi 2004; Hendler 2004; Mercer 2008) and much more likely to have vaginal births (Cameron 2004; Caughey 1998; Flamm 1997a; Gonen 2004; Gyamfi 2004; Hendler 2004; Kwee 2007; Landon 2005; van der Merwe 2013). Limiting analysis to the second delivery also fails to consider the risks of accumulating cesareans (Cook 2013; Guise 2010; Makoha 2004; Nisenblat 2006; Silver 2006), which should be part of the equation. Women may plan only two children, but plans may change and life may hand us surprises.

The study’s primary outcomes were composites of severe maternal (postpartum hemorrhage requiring transfusion or procedures to control bleeding, disseminated intravascular coagulation, cardiac arrest, cardiopulmonary resuscitation, acute myocardial infarction, heart failure, pulmonary edema, cardiac complications from anesthesia, assisted ventilation, adult respiratory distress syndrome, renal failure, repair of injury to bladder or urethra, and maternal death) and neonatal (seizures, assisted ventilation of any kind, and neonatal death) morbidity and mortality. Investigators also evaluated the same maternal composite leaving out transfusion, the most common severe morbidity and, I would add, one that shouldn’t deter VBAC because it has no ongoing consequences. In addition, they looked at certain maternal outcomes individually such as scar rupture and hysterectomy. Similarly, investigators evaluated a secondary neonatal composite limited to the most severe outcomes (neonatal death, seizures, and assisted ventilation requiring endotracheal intubation) and looked at certain outcomes, such as neonatal death and respiratory distress syndrome, separately.

This brings us to problem number two: the low VBAC rate. VBAC rates hovered around 50% throughout the time period. Complications and adverse outcome rates depend heavily on VBAC rate because they almost all occur in labors that end in cesarean or in which women experience scar rupture (Landon 2004). The lower the VBAC rate, the worse VBAC looks compared with planned cesarean, and a 50% VBAC rate is dismal compared to what can be achieved. Rates have ranged from 61% to 72% in women with no prior vaginal births in studies of obstetrician-attended VBACs (Agnew 2009; Cahill 2006; Cameron 2004; Caughey 1998; Flamm 1997; Goodall 2005; Gyamfi 2004; Hendler 2004; Kwee 2007; Landon 2005; Srinivas 2007; Turner 2006) and reached 81% in studies of midwife-attended VBACs (Cheyney 2014; Lieberman 2004).

We don’t know what influenced the Canadian doctors’ decision making, but a large, multi-center U.S. study is revealing: 1/3 of women who had repeat cesareans for progress delay or failed induction had them before 5 cm dilation, and over half had them before 6 cm, which means they were still in latent labor (Zhang 2010). Slow progress should rarely be an indication for cesarean in this phase of labor (ACOG & SMFM 2014). We also know that clinician bias affects decisions. Investigators in another study noted that women whose prior cesareans were for progress delay were given 2 to 2 ½ hours less time in the VBAC labor than women whose prior cesarean was for concern about the baby or breech (Shipp 2000). These are the very women who might need more time, not less.

Next, we come to labor management. Thirteen percent of women planning VBAC had labor induction. Induction is a double whammy. It increases the odds of scar rupture, especially when prostaglandin E2 is involved (misoprostol is contraindicated in VBAC labors) (Bujold 2004; Delaney 2003; Flamm 1997; Hoffman 2004; Kayani 2005; Kwee 2007; Landon 2004; Lin 2004; Ravasia 2000; Zelop 1999), and induction with cervical ripening reduces likelihood of vaginal birth (Agnew 2009; Ben Aroya 2002; Bujold 2004; Delaney 2003; Elkousy 2003; Flamm 1997; Gonen 2004; Goodall 2005; Grobman 2007; Gyamfi 2004; Hoffman 2004; Kwee 2007; Locatelli 2004; Ouzounian 2011; Ravasia 2000; Srinivas 2007; van der Merwe 2013). In addition, doubtless, some proportion of the VBAC population had augmentation. That increases odds of scar rupture too (Dekker 2010; Kwee 2007; Landon 2004).

So, what were the differences in outcomes?

Starting with maternal outcomes, 11 per 1000 women having a VBAC labor experienced one or more of the composite outcomes compared with 6 per 1000 in women having planned repeat cesareans, or 5 more women per 1000. Removing women whose only adverse outcome was requiring a transfusion, 7 women per 1000 having VBAC labors experienced one of the composite outcomes versus 5 women per 1000 in the planned cesarean group, a difference of only 2 per 1000. 7 women per 1000 who birthed vaginally experienced a severe adverse outcome compared with 6 women per thousand in the planned cesarean group, a clinically insignificant difference, and excluding transfusion, the percentages were 2 per 1000 having VBAC versus 5 per thousand having planned cesarean, or 3 more with planned cesarean than in women having vaginal birth, which affirms that as the percentage of women having a vaginal birth increases, the better VBAC will look.

Scar rupture rates were low, occurring in 3 per 1000 VBAC labors. Even in labors ending in cesarean, the scar rupture rate was only 6 per 1000, which means that few cesareans in the VBAC group would have been because of scar rupture. In women birthing vaginally, it was 5 per 10,000, the same rate as in women having planned cesarean. Among women having a hysterectomy, the only severe morbid event with permanent consequences, rates were identical in both women planning VBAC and in women having planned cesarean at 6 per 10,000. Hysterectomy rates, however, increase markedly with increasing numbers of repeat cesareans (Guise 2010), and, I should add, so do rates of other severe complications such as bladder and bowel injury during surgery (Cook 2013; Makoha 2004; Nisenblat 2006; Silver 2006), doubtless because of the increasing prevalence of dense adhesions (Guise 2010). As for maternal mortality, I assume that no women died in either group as that would surely have been reported separately by investigators.

Turning to the baby, the neonatal mortality rate was 2 per 10,000 in women planning VBAC. Canada’s national neonatal mortality rate, it should be noted, was 6 per 10,000 in 2013 and 2014. 21 per 1000 babies whose mothers had VBAC labors experienced one or more adverse outcomes in the composite compared with 15 per 1000 whose mothers had planned cesareans, a difference of 6 per 1000. Differences shrank in the composite restricted to the most severe morbidity and mortality: 7 per 1000 for planned VBAC versus 4 per 1000 for planned cesarean, or 3 more per 1000, not exactly a compelling argument for elective repeat cesarean, especially considering the hazards for future pregnancies of accumulating cesareans. And then there’s the other side of the coin: babies were less likely to experience respiratory distress syndrome in the planned vaginal birth group (49 per 1000) and much less likely to experience it in labors ending in vaginal birth (37 per 1000) than in women having planned cesareans (55 per 1000), another demonstration that improving the vaginal birth rate in VBAC labors would tip the scales toward planned VBAC.

Investigators also explored whether outcomes changed over the years. Comparing outcomes from 2003 to 2005 with outcomes from 2012 to 2014, they found no differences in maternal severe adverse outcomes, but neonatal severe morbidity and mortality trended upward. Planned VBAC was not associated with worse neonatal outcomes in the 2003 to 2005 cohort, but it was in the 2012 to 2014 group. The investigators theorize that this may be due to less rigorous selection of candidates—although neither the percentage of women laboring nor the percentage who had vaginal birth changed over the years of the study, changes in maternal characteristics over time, or changes in management.      

Addressing the worsening of neonatal outcomes over time, investigators conclude with the vague recommendation to take greater care in selecting candidates and in monitoring labor and delivery, thereby centering the problem in women. But, in reality, the problem is not the fault of the women who go on to birth after a cesarean. What’s needed is a hard look at what policies and practices improve VBAC safety and success and implementing them universally. This is the responsibility of the health care providers setting up facility guidelines. Even with things as they are, though, because of the dangers of multiple cesareans, I stand with the authors of Evidence-Based Maternity Care: What It Is and What It Can Achieve who wrote (Sakala 2008):

As many women will have additional children, future childbearing is difficult to predict, and hazards increase as the number of previous cesareans grows, it would be wise for women without a clear and compelling need for cesarean section in the present pregnancy to avoid the extra risks of surgery and to get off the repeat cesarean track.

References

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About Henci Goer

Henci Goer, award-winning medical writer, and internationally known speaker is an acknowledged expert on evidence-based maternity care. Her first book, Obstetric Myths Versus Research Realities, was a valued resource for childbirth professionals. Its successor, Optimal Care in Childbirth: The Case for a Physiologic Approach, won the American College of Nurse-Midwives “Best Book of the Year” award. Goer has also written The Thinking Woman's Guide to a Better Birth, which gives pregnant women access to the research evidence, as well as consumer education pamphlets and articles for trade, consumer, and academic periodicals; and she posts regularly on Lamaze International’s Connecting the Dots. Goer is founder and director of Childbirth U, a website offering narrated slide lectures to help pregnant women make informed decisions and obtain optimal care for themselves and their babies

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