A multiple pregnancy is usually a contraindication to a VBAC
Written by Assoc Prof Mark Umstad, AMBA Patron, and published in the AMBA Magazine
The rate of caesarean section has steadily increased in Australia over the past few decades. The caesarean section rate is now around 30% for singleton pregnancies, around 70% for twin pregnancies and virtually 100% for triplet and higher order multiple pregnancies.
There are several reasons for this steady increase. Firstly, women are having babies at a later age and there is no doubt that increasing maternal age has a negative impact on the effect of uterine contractions during labour. This means that as women get older, their labour becomes less effective and the risk of caesarean section increases. Secondly, there has been a steady increase of obesity throughout the entire western world. Obesity is strongly linked with an increased risk of caesarean birth. As weight almost inevitably will increase over the next few decades, we can expect to see the caesarean section rate continue to climb. Finally, obstetricians are less frequently conducting what would previously have been considered quite complicated births. This includes vaginal breech deliveries, vaginal twin deliveries and forcep deliveries, that are anything other than a very straightforward procedure. When a woman has had a previous caesarean section for any reason, obstetricians then need to carefully consider the most appropriate method by which the next baby should be delivered. The rates of repeat caesarean section in Australia are in the order of 60% to 80% and as high as 90% in the United States. The proportion of women who successfully deliver vaginally after caesarean section (VBAC) varies between 40% and 80% depending on how actively the procedure is promoted.
Risks of repeat elective caesarean section
If women have a repeat elective caesarean section, they are at increased risk of surgical complications such as a wound infection, and their babies have a slightly higher risk of breathing difficulties after birth. If infection complicates the birth, then there is a risk of subsequent infertility. It must also be considered that with increasing numbers of caesarean sections comes a higher risk of a condition known as placenta accreta. In this condition, the placenta grows into the previous caesarean section scar and can cause very serious complications, often requiring a hysterectomy in a subsequent pregnancy. However, it must be recognised that the risk of this condition is extremely low.
Risks of VBAC
The results of a recent Australian study from Professor Dekker and colleagues have provided us with very contemporary evidence of the risks of VBAC following one prior caesarean section. For women who have had a previous caesarean section and have not laboured, the risk of uterine rupture is about 0.01%. If labour occurs spontaneously, the risk is 0.15%; if labour has already started and oxytocin is used to increase the strength of the contractions, it rises to 1.91%. If labour has not yet started and is induced with oxytocin, the risk of rupture is 0.54%; if prostaglandins are used it is 0.68% and if both prostaglandins and oxytocin are used it is 0.88%. Compared with spontaneous labour, risks are increased 3- to 5-fold for any induction, 6-fold for prostaglandins combined with oxytocin and 14-fold for augmentation with oxytocin.
The consequences of a uterine rupture can be very significant. If it occurs there is usually significant bleeding, a high likelihood of needing a blood transfusion, a small chance of needing a hysterectomy to control the bleeding, and a risk of either brain injury or death of the baby. Although these are confronting issues to consider, these are the very issues that obstetricians consider in advising for or against VBAC. The risk of losing a baby during delivery by repeat elective caesarean section is 0.01% compared with 0.13% following an attempted VBAC. The risk of the baby suffering a brain injury during the process is virtually zero in a repeat elective caesarean section and around 0.1% following a VBAC. Of course these numbers are very small, but it must be considered that the risk of either losing a baby or the baby suffering a brain injury or dying is about 10 times higher after VBAC than after caesarean section.
There are certain circumstances that are absolute contraindications to a VBAC. These include a previous classical caesarean section (with a vertical incision), a previous uterine rupture, or a medical or obstetric condition that precludes vaginal delivery such as placenta praevia.There are other factors that obstetricians will strongly consider as reasonable reasons to avoid a VBAC. These would include two or more previous caesarean sections, a particularly large baby and when an induction is required. There are several very small studies of women having twins delivered by VBAC. The studies are too small to draw any strong conclusions about the risk or safety of such a procedure, but most obstetricians would generally consider that multiple pregnancy is a contraindication to a VBAC.
Management in labour
Having decided on undergoing a VBAC, and recognising the risks that can occur with such a procedure, it is important to be able to minimise any consequences, should complications arise. The first principle is that a VBAC should only be conducted in a hospital where there is immediate access to emergency resources. If a uterine rupture does occur, it becomes a major obstetric emergency, which will involve operating theatres, anaesthetists, midwives, paediatricians, obstetricians, blood transfusion facilities as well as potentially an intensive care unit. It is very important that, if you are planning on undertaking a VBAC, you ensure that these facilities are available to maximise the safety for yourself and your baby. The general principles of management in labour would require the insertion of an intravenous drip; blood is taken to be sent to the bloodbank, so it is available for transfusion should it be required. Continuous electronic foetal heart rate monitoring in labour is essential as it can provide an early sign that the scar is potentially going to rupture. This warning may only be 30 to 60 seconds, but may be very helpful to your obstetrician. It would be usual for regular vaginal examinations to be performed and for the waters to be broken by your obstetrician. It is not absolutely contraindicated to use either prostaglandins or oxytocin to induce or augment labour, and indeed many obstetricians have this preference. However, as described above, it does increase the risk of scar rupture and needs careful consideration. Slow progress in labour is generally considered by most obstetricians to be an indication to abandon the VBAC and proceed to an emergency caesarean section. Forceps and ventouse (vacuum) deliveries can still be performed as normal. Epidurals do not mask the signs of uterine rupture and can be safely used.
The caesarean section rate in Australia will continue to climb and an increasing number of women will need to consider VBAC as an option. There are risks associated with a VBAC. Although these risks are relatively low, the consequences can be quite severe, which is the reason why many women choose not to pursue this option. Facilities for emergency delivery must be available if a VBAC is attempted.
References: Dekker G, Chan A, Luke C, Priest K, RileyM, Halliday J, King J, Gee V, O’Neill M, SnellM, Cull V, Cornes S. Risk of uterine rupture in Australian women attempting vaginal birth after one prior caesarean section: a retrospective population-based cohort study. BJOG 2010;117:1358-1365.