VBAC safety

I retired last December, having been a student and Trainee in the 1960s and early 1970s. After MRCOG training in the UK, I returned to Australia and, over the course of my working life, became increasingly concerned about the lack of understanding of the lower segment not only among students, but also many registrars and even a generation of consultants. Fortunately, there seems to be some improvement of this understanding, but my observation is that this is not well applied in practice and, I believe, contributes to the risk of uterine rupture at vaginal birth after caesarean (VBAC).

During my training we were taught a physiological difference – the lower segment being passive and the upper segment being active – was the key to the safety of the lower segment caesarean section (LSCS) operation compared to the upper segment or classical caesarean. This reasoning explained the potentially catastrophic effects of rupture of the upper segment and the safety of LSCS, which was said to dehisce in a quiet and safe manner, requiring repeat caesarean but not causing other dangers. For some time after, I corrected registrars when they referred to uterine rupture, a more dangerous event than dehiscence, as a risk of VBAC, but have since become aware that the term ‘rupture’ can indeed be justified in this context.

My own experience during my training years and the first part of my specialist career here, when the VBACs I conducted were on patients whose first caesarean had been done by me or an older colleague with similar operative technique, was that on the very few occasions that a scar came apart it had indeed only dehisced, usually partially, and no harm ensued other than the caesarean being repeated. This statement can be dismissed as anecdotal, but surely observations from more than four decades’ busy experience in training and independent practice should count for something.

Thoughts I tried to convey to my Trainees included:

• I would have had my knuckles rapped very smartly if during my training I made the transverse uterine incision as high as is commonly seen today. The lowest part of this incision is usually done a bit on the high side so the lateral parts very definitely extend higher into the uterus than would have been acceptable when I trained. I have tried to find published literature comparing the results of the muscle splitting transverse incision I was taught with the upward curved incision, but was only able to find comparison of blood loss, the smiley incision usually having just a bit less, rather than studies comparing outcome of VBAC in subsequent pregnancies.
• An appreciation that the lower segment forms in the latter part of pregnancy as the uterus stretches. This has become more significant in recent years as neonatologists are getting ever better results with younger fetuses and an increasing number of caesareans are performed for premature infants. I was pleased that in the latter part of my career many (but by no means all) of my colleagues started to recognise that LSCS done early in pregnancy, last I heard it was before 34 weeks, were not suitable for attempts at VBAC as the lower segment is not properly formed before this time.
• In many places, in the laudable interest of offering choice, a woman who has had a previous caesarean when presenting for antenatal care will often have VBAC discussed/offered by the midwife who is the person of first contact before any review by an obstetrician. Thus there will often be pressure for or offers of VBAC in a population not screened for suitability or otherwise of this option. I have had a few very angry patients who were not at all happy to be told that they were not suitable candidates for VBAC. We can give in to their unrealistic requests, but we accept the responsibility. Satisfaction, or lack of it, with obstetric outcomes depends on how the outcome compares to the expectation more than the outcome itself.
• Failure to obtain operative notes of the primary caesarean is alarmingly common. Without the operative notes one cannot even be sure that the initial operation was LSCS, as there are many who still think that the sign of a LSCS is a Pfannenstiel abdominal scar and that a classical caesarean is indicated by a sub-umbilical vertical midline scar. The operative notes will confirm an uneventful operation or otherwise, for example, the occasional inverted-T or J-shaped extension of an incision or other operative difficulties. This means going to the effort of requesting a copy of the actual operation record, not just a discharge summary. In some places, such as parts of China, classical caesareans are still the routine so one can never assume that the primary operation was an uneventful LSCS.

All this can be dismissed as the anecdotal ravings of a sad, old has-been and it could be suggested that the reason we didn’t see ruptures, as opposed to dehiscences, was that the caesarean rate was much lower. Nevertheless, we saw enough to all have seen several dehiscences. It should also be borne in mind that the rupture rate of VBAC after true classical caesarean is only around 20 per cent. I am personally convinced that if the above precautions were to be generally observed true LSCS would regain significant safety. Prospective studies would be very hard to do with our mobile population, are there any studies looking at details of the previous caesarian in cases of uterine rupture at VBAC?