One of the most common dictums in obstetrics was put forward almost a century ago by Edwin Craigin: ‘once a caesarean always a caesarean’. The main purpose of Craigin’s presentation was to point out the maternal risks of caesarean section with a plea that it should be used only for the most stringent indications. In the early 20th century the most common indication for caesarean section was disproportion and contracted pelvis, and the type of caesarean section was classical with its associated significant risk of uterine rupture in a subsequent pregnancy. Thus, when Craigin proposed his dictum it was appropriate, as it would be now under the same circumstances. Craigin’s main point was that caesarean section was a dangerous operation and that once it was performed the woman would be subject to the dangers of repeat caesarean section in a subsequent pregnancy. He did, however, point out that vaginal delivery after previous caesarean section was feasible and reported one of his own patients who had three vaginal deliveries after one caesarean section.
‘One thing must always be borne in mind, viz., that no matter how carefully a uterine incision is sutured, we can never be certain that the cicatrized uterine wall will stand a subsequent pregnancy and labor without rupture. This means that the usual rule is, once a Caesarean always a Caesarean. Many exceptions occur … The general rule holds, however, that we cannot depend upon a sutured uterine wall, whether it is done in a Caesarean section or a myomectomy, hence I believe the extension of Caesarean section to conditions other than dystocia from contracted pelvis or tumours should be exceptional and infrequent.’
Edwin Craigin
Conservatism in obstetrics. NY Med J 1916; 104:1–3
As the low transverse caesarean section became more common in the 1930s and 40s, and the indications for caesarean section widened to include non-recurrent reasons, the approach to women previously delivered by caesarean section changed in many countries. The risk of subsequent rupture of low transverse caesarean section was small and increasing numbers of women were encouraged to undergo labour and vaginal delivery. By the late 1970s and 1980s there were many reports of large series showing that spontaneous labour and vaginal delivery following a single low transverse caesarean section was a safe and reasonable option with appropriate safeguards. Consensus statements embraced and encouraged labour and vaginal delivery with a previous caesarean section under these circumstances.
However, as is so often the case in obstetrics, the pendulum of opinion swings too far and labour and vaginal delivery was pursued for widening indications – including more than one previous caesarean section, induction of labour and augmentation of non-progressive labour. Not surprisingly, an increasing number of cases of uterine rupture were reported, some of which resulted in fetal death or severe neonatal neurological damage, as well as maternal morbidity, sometimes including hysterectomy. The possibility of complete uterine rupture in labour ranges from 3 to 7 per 1000 pregnancies, while the risk of perinatal death or severe morbidity, should rupture occur, is 4.5 per 1000 more with trial of vaginal delivery than with repeat caesarean delivery. These rare but tragic outcomes and the associated medico-legal sequelae caused the pendulum to swing rapidly back in the opposite direction. Revised national guidelines suggested more stringent facility and personnel requirements in order to conduct labour and vaginal delivery following previous caesarean section. Some hospitals, fearing institutional liability, forbade labour and vaginal delivery following previous caesarean section. The most sensible, practical and safest clinical course lies in the middle ground.
The term ‘trial of labour’ has been applied incorrectly to these cases. Trial of labour is a well-established obstetric principle when labour is undertaken in the face of suspected disproportion, which is contraindicated in a woman with a uterine scar. The term ‘trial of scar’ should also be avoided. The correct term is ‘trial for vaginal delivery’.
This chapter will outline the factors that need to be considered in helping women reach a decision whether or not to undertake labour with a view to vaginal delivery after previous caesarean section.
Selection Criteria for Vaginal Birth after Caesarean Section (VBAC)
The previous obstetrical record should be reviewed so that details of the labour, indications for caesarean section, operative details and postoperative recovery can be appraised. There are several factors that need to be evaluated in assessing the level of medical risk and, indeed, medico-legal risk so that the appropriate informed consent can be obtained.
Type of Uterine Scar
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Classical caesarean section scars are about 10 times more likely to rupture during labour than lower segment caesarean incisions and may rupture before the onset of labour. The rupture rate for a previous classical scar is approximately 3–5%. In addition, this type of scar rupture is potentially much more lethal to both fetus and mother as it tends to give way suddenly and this may be before labour or early in labour. As a result the woman is often not in hospital when the rupture occurs. This is in contrast to the lower segment caesarean scar which is most likely to rupture after some hours of labour when the woman is in hospital and appropriate medical intervention can be undertaken without delay.
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Low vertical caesarean section is rarely performed. The indication is usually in earlier gestation when the lower uterine segment has formed to a degree but its transverse dimensions are felt to be inadequate for the normal transverse incision. In these cases the low vertical incision has been advocated as an alternative to classical caesarean section. However, in many instances the lower segment is not sufficiently developed, even vertically, to allow a big enough incision without encroaching on the upper uterine segment. Thus, these scars, while having a slightly smaller risk of rupture than a classical caesarean scar, are probably best treated in the same manner.
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Extensions of a transverse lower segment caesarean incision should be appraised by careful scrutiny of the operative report. If there was any marked extension of one or both angles, or a ‘T’ extension into the upper uterine segment, these scars are best not subjected to labour.
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Hysterotomy scars are not commonly seen in modern obstetrics with medical methods for second trimester termination. However, if present they should be treated in the same manner as a classical caesarean scar and repeat elective caesarean section chosen.
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Myomectomy incisions require individual consideration. If the incisions are extensive, and particularly if the uterine cavity was entered, they are probably best not subjected to labour. Similarly, hysteroscopic myomectomy incisions, if associated with perforation of the uterus would be best managed by elective caesarean section. Otherwise, hysteroscopic myomectomies not associated with perforation or deep myometrial excision can be allowed to labour.
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Previous rupture of any type of uterine scar in a previous pregnancy is obviously a contraindication to subsequent labour.
In some cases it is impossible to obtain the previous operative record. From the history it is often possible to work out the type of the previous uterine incision. For example, if the previous caesarean section was done at term, and particularly if it was for dystocia, one can reasonably assume that it was a transverse lower segment caesarean section. On the other hand, if the caesarean section was done at less than 32 weeks’ gestation and not in labour the chances are more likely that a classical caesarean section was done. Augmentation of labour with oxytocin in the latent phase with an unknown uterine scar has been associated with an increased risk of uterine rupture and dehiscence.
Labour with the Previous Caesarean Section
If the previous caesarean section was carried out electively without labour, or in the early latent phase of labour, the pattern of uterine activity in the subsequent labour is likely to be of the nulliparous type, requiring stronger and longer uterine work to efface and dilate the ‘nulliparous’ cervix. In contrast, those who had previous caesarean section in active labour are more likely to show a multiparous pattern in a subsequent labour, with less uterine work and less strain on the uterine scar.
Previous Vaginal Delivery
If the woman had a previous vaginal delivery, either before or after the caesarean section, her chances of a successful and safe VBAC are enhanced. This is one of the most positive factors in favour of trial for vaginal delivery.
Uterine Incision Closure
One large retrospective review showed a significant increase of subsequent scar rupture in those women in whom the initial caesarean had a single-layer versus a double-layer closure. However, this finding has not been noted in other hospitals and there are many who have not shown an increase in scar rupture rates or changes in infectious morbidity since changing to single-layer closure.
Postoperative Infection
Postpartum endomyometritis may interfere with adequate healing of the uterine scar and increase the risk of subsequent rupture in labour. The practical clinical point here is that many cases of postpartum fever are not due to endomyometritis. Thus, it is inappropriate to exclude all women who have had a postpartum fever following the previous caesarean delivery. However, if there is good clinical evidence in the record that the sepsis was intrauterine it may be prudent to avoid labour in a subsequent pregnancy.
Recurrent Indications for Caesarean Section
One of the most common reasons for primary caesarean section is dystocia or cephalo-pelvic disproportion, although a true diagnosis of the latter is rare. These diagnoses are not necessarily a recurrent indication and many will labour and deliver successfully after a previous caesarean for these indications. Overall, however, they have a slightly lower success rate than for other ‘non-recurrent’ indications.
Inter-Pregnancy Interval
Pregnancy and delivery within 12 months of a previous caesarean section may be associated with an increased risk of scar rupture in that pregnancy.
Twins
A large cohort study suggests risks of uterine rupture with trial for vaginal delivery after caesarean are similar between twin and singleton pregnancies. However, to some extent twin pregnancies have potentially double the price to pay for subsequent scar rupture. In addition, over-distension of the uterus associated with multiple pregnancy and the possible need for intrauterine manipulation for delivery of the second twin increase the risk of scar rupture. These are cases in which other selection criteria and individual considerations have to be weighed very carefully and cautious prudence remains the guiding principle.
External Cephalic Version
The influence of manoeuvres required for external cephalic version (ECV) on the uterine scar is unclear. Uterine rupture is a theoretical risk but has not been well studied. Rates of successful ECV are similar between women with a previous caesarean section and women without a previous caesarean section.
More than One Previous Caesarean Delivery
There are a number of series that have shown success in achieving vaginal delivery in women with two previous caesarean sections. However, the risk of uterine rupture is approximately doubled and the woman should be so informed.
Measurement of Lower Uterine Segment Thickness
Small studies using ultrasound to measure the thickness of the lower uterine segment in the third trimester of pregnancy have suggested that those women with a very thin lower uterine segment have an increased risk of scar rupture. This work is promising and it is possible that there may be a critical measurement below which trial for vaginal delivery carries too great a risk.
Predicting Adverse Outcomes with Trial for Vaginal Delivery
Validated antepartum prediction tools demonstrate an association between increasing maternal age and post-term pregnancies with an increased risk of emergency caesarean section and uterine rupture in women planning vaginal birth after previous caesarean section.
Hospital Facilities and Personnel
Trial for vaginal delivery can only be undertaken in a hospital which has immediately available midwifery, nursing, anaesthesia and obstetric staff along with the appropriate operating theatre, laboratory and blood transfusion services. These criteria have been reviewed in national guidelines.
Decision Aids for Mode of Delivery
Randomized controlled trial data using computer-based decision aids, given to women with a previous caesarean section and their health care professional, demonstrate a reduction in decisional conflict and higher rates of vaginal delivery compared to usual care. The decision aids allowed access to standardized and reliable information and empowerment of the user.
Cost
Caesarean delivery in labour has been shown to be associated with increased costs compared to spontaneous delivery and to caesarean delivery without labour. Studies modelling cost-effectiveness demonstrate that the average expected cost of failed trial for vaginal delivery is higher than either vaginal delivery or elective repeat caesarean delivery. If the a priori chance of a successful trial for vaginal delivery is at least 74%, then the cost/benefit profile favours a trial for vaginal delivery.
There are a number of so-called ‘soft factors’ which, in addition to the above, may influence the decision. These include maternal age, maternal obesity, secondary infertility, the desire for more pregnancies and previous maternal morbidity.
It is essential that the woman and her partner understand and accept the principles involved in a trial for vaginal delivery. From a review of the above selection criteria certain increased risks may be identified and these must be discussed with the woman, along with the advantages of a successful trial for vaginal delivery. It is quite inappropriate to apply any coercion, however subtle, towards labour.
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