Is CTG monitoring “essential” during VBAC?

Woman planning vaginal birth after caesarean section (VBAC) are sometimes told that CTG monitoring is “essential” because of the risk of uterine rupture (like this advice from Safer Care Victoria). Let’s explore why this is nonsense.

Can CTG monitoring prevent uterine rupture?

No. Just like having air bags installed in your vehicle will not prevent an accident from happening, CTG monitoring can’t prevent uterine rupture.

During labour the uterus is either intact (not ruptured) or there is a tear in it (ruptured). After uterine rupture occurs, there are symptoms that the woman might notice herself (like severe pain and vaginal bleeding) and signs that a maternity professional might detect (like the woman’s blood pressure is low and her heart rate is fast). One of these signs is a change in the fetal heart rate pattern. This collection of symptoms and signs lead to the diagnosis of uterine rupture being suspected clinically. Performing surgery confirms the diagnosis when the tear in the uterine wall is seen.

The only way the CTG contributes to the clinical suspicion of uterine rupture is when changes in the fetal heart rate happen, and these only happen after the rupture has occurred, in response to falling oxygen levels caused by damage to the placenta or reduced blood flow to the woman’s uterus. At best then, seeing an abnormal heart rate pattern with CTG monitoring might reduce the time between when the uterus ruptures and when surgery is performed to confirm the diagnosis and treat the issue. So – what evidence is that that CTG monitoring leads to early detection of uterine rupture?

Abnormal heart rate patterns and uterine rupture

Let’s begin by noting that there is no special heart rate pattern that happens with uterine rupture, one that is distinctly different to other heart rate patterns. The changes seen with uterine rupture are the same physiological response to low oxygen levels that aims at preventing or reducing fetal injury, that are seen with any other cause for low oxygen levels for the fetus.

Two recent research studies, one from France (Dessauve et al., 2016) and the other from Denmark (Andersen et al., 2016) have looked at what patterns are most commonly seen in the time prior to a diagnosis of uterine rupture. Andersen and colleagues showed that tachycardia (a fast heart rate) and more than ten severe decelerations in a thirty minute period were common, with a very abnormal CTG being present for 77% of women with uterine rupture. On the other hand, Dessauve and colleagues found that bradycardia (a slow heart rate) was common, and heart rate patterns were abnormal for 82% of women with uterine rupture.

While the abnormal heart rate patterns in these studies were detected with CTG use, that was because it is far easier to retrospectively analyse the CTG than to review records about intermittent auscultation, and because CTG monitoring is what is used most commonly during women’s attempts at vaginal birth after caesarean section. The common patterns they described are all easy to detect with intermittent auscultation, making it unlikely they would be missed if regular intermittent auscultation was in use.

What this looks like in practice…

Both these studies found that abnormal heart rate patterns happened more often with uterine rupture than they did during labour for women with a prior caesarean section who did not experience uterine rupture. In women who didn’t experience rupture the rate of abnormal heart rate patterns was lower – 25% (Desseauve et al., 2016) and 53% (Andersen et al., 2016). This reads as though it would be very easy tell the women with uterine rupture from the ones without. Let’s use the numbers from the French study and I’ll show you why that is far from the truth.

Say 1,000 women attempt vaginal birth after caesarean section and five experience uterine rupture rupture (this was the rate reported from the Danish Birth Registry used by Andersen et al.). Four of the women (82%) with uterine rupture will have an abnormal CTG. That leaves 995 women who do not experience uterine rupture, and 25% of this is 249, the number of women without uterine rupture who will have an abnormal CTG pattern. So out of 253 women with an abnormal CTG pattern, 4 or 1.6% will have a uterine rupture and 98.4%, the vast majority, will not. (If you use the numbers from the Danish research, the proportion of women with an abnormal CTG who have uterine rupture is even smaller, at 0.8%).

So, when attempting to decide whether or not the CTG is abnormal due to uterine rupture or not, and whether immediate action is appropriate or not, maternity professionals MUST look for other clinical signs / symptoms and weigh up the woman’s other risk factors as they decide on the most appropriate course of action. So even though abnormal heart rate patterns are the most common sign of uterine rupture, the heart rate pattern is never, ever, considered in isolation to the rest of the clinical picture.

So, no – CTG monitoring is not “essential” with VBAC

There is absolutely no proof that women who choose intermittent auscultation for their vaginal birth after caesarean section will miss out on their maternity professional being able to diagnose uterine rupture in a timely manner. CTG monitoring is not “essential”, “needed”, “mandatory”, or “required”. The decision about which form of heart rate monitoring to use (or the decision to have none at all) rests entirely with the woman giving birth.

Are you planning a vaginal birth after caesarean section and are looking for more information about the fetal monitoring options available to you? I have a course designed just for you!

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References

Andersen, M. M., Thisted, D. L., Amer-Wahlin, I., Krebs, L., & Danish CTG Monitoring during VBAC study group. (2016). Can intrapartum cardiotocography predict uterine rupture among women with prior caesarean delivery?: A population based case-control study. PLoS ONE, 11(2), e0146347. https://doi.org/10.1371/journal.pone.0146347

Desseauve, D., Bonifazi-Grenouilleau, M., Fritel, X., Lathélize, J., Sarreau, M., & Pierre, F. (2016). Fetal heart rate abnormalities associated with uterine rupture: a case–control study. European Journal of Obstetrics & Gynecology and Reproductive Biology, 197, 16-21. https://doi.org/10.1016/j.ejogrb.2015.10.019