Are VBACs really risky?

Are VBACs really risky?


In order to consider the possible risks of a VBAC, researchers have compared what happens with women who have a VBAC with those who have another caesarean. In order to do this, they usually track how many women have what is called a uterine rupture—i.e. a separation of the uterine incision, which is the basic risk of a VBAC. They also consider in numerical terms what the consequences are (with either a VBAC or a caesarean) for the health of both mother and baby.

Since before the 1950s, it has been widely accepted that having a VBAC is basically a safe option in the majority of cases—except in North America—and that the specific risk which a VBAC presents is that of uterine rupture. The assessment of the basic risk a VBAC involves has not changed since scientific reviews of research were carried out in the 1980s. At the first consensus conference at that time,3 VBAC was recommended in cases where the woman had previously had a single, low, transverse incision, and when she was expecting just one baby in her subsequent pregnancy, which was in a headdown position. WHO emphasises that it is not necessary for a woman to have a repeat caesarean in the majority of cases.4 In Britain, NICE states that “Pregnant women who have had a previous caesarean and who want to have a vaginal birth should be supported in this decision.”5


In order to consider this risk for this book I looked mainly at the kind of scientific evidence which is considered most ‘robust’ and reliable in medical circles: systematic reviews of research, meta-analyses and large-scale studies— i.e. studies which look at large numbers of people—which were carried out from 1990 onwards. I also consulted key people in professional, medical or paramedical associations.

Before considering this research, let’s consider what uterine rupture actually is… Here, we are talking about the situation where the uterine incision (from a previous caesarean) opens up. This is a serious—but uncommon— problem, when it occurs, because it can cause complications for both mother and baby. In fact, when it occurs, it’s a real emergency and the mother has to be taken into surgery immediately so that her baby can be extracted and her uterus repaired.

Next—before considering the research relating to the risk of uterine rupture during a VBAC—we need to remember that, in fact, the risk of the uterus rupturing exists in any pregnancy where the woman has previously had a caesarean. Many people don’t realise that having a repeat elective caesarean does not protect women from this risk… After all, although the risk is very low, a uterine rupture could occur even before the woman goes into labour.

Before we turn our attention to the research, we also need to recognise that most separations of uterine incisions, which were for a long time the focus of research studies, are actually cases of ‘dehiscence.’ This means a defect or opening in the uterine scar, rather than a separation of all layers. Several studies failed to differentiate between rupture and dehiscence, which makes it difficult to clearly interpret the research data.6 The term ‘fenestrated’ also occurs in the research data, a term which means that a ‘window-like’ opening exists—which is the most benign type of opening up. This is a hole in the uterine incision which occurs when scar tissue is forming and it is not problematic. It is nevertheless detectable during an examination of the uterus during a subsequent caesarean. The separation of tissue which is called ‘dehiscence’ means that in one place the layers of the uterus are no longer welded together—a little like the layers of a flaky pastry! (This can be seen in cross-section, by ultrasound.) Nevertheless, in this kind of ‘rupture’ muscle tissue remains, even though it is thin—and there is no real separation of the uterine incision. Usually, the membranes do stay intact, there is no bleeding, no pain and the fetus remains inside the uterus. A dehiscence is therefore not dangerous in the same way as a rupture and does not necessarily need to be repaired. Like fenestration, it is again usually only detected during a repeat caesarean. Other expressions are also used to refer to other things (apart from rupture), but less frequently, such as thinning of the uterine wall because there could be an increased risk of rupture when the thickness of the uterine wall (at the uterine incision scar) measures less than 2.3mm to 2.5mm.7 But, again, studies do not differentiate between these when they consider the prevalence of rupture.8 But if it is a real rupture, what does it actually involve? The risk for the mother in the case of a real rupture really relates to the risk of haemorrhage and of having a hysterectomy.

You might ask at this point how it is possible to differentiate a real rupture from one of these other, less dangerous types… What are the symptoms of a real uterine rupture? According to Flamm (2001),9 the most reliable sign that a uterine rupture is occurring is one or more prolonged deceleration of the fetal heartbeat (bradycardia)—for example, a decrease to 60-70 beats per minute or less, over a period of several minutes, with no variation when the fetal heart is stimulated by a maternal change of position. Other signs include a significant regression in the fetal station (i.e. the baby’s amount of descent through the pelvis) or substantial vaginal bleeding. Flamm emphasised that other symptoms which have been the focus of attention are only weak signs of rupture—e.g. maternal tachycardia (when the mother’s heart beats faster than normal), lowering of blood pressure (i.e. arterial pressure), blood in the urine and severe pain. However, he notes that we should not forget that 15 minutes after an epidural has been administered a significant lowering of the fetal heart rhythm may occur. This usually improves quickly, but may be frightening to parents-to-be and medical staff. Beyond these signs which can be observed at the moment a rupture is occurring, as yet, no way has been discovered of determining in advance whether or not a uterine rupture is likely to occur.

From Helene Vadeboncoeur's book, Birthing Normally After a Caesarean or Two.