Trying labour to achieve a vaginal birth after having a previous caesarean section is certainly an option. There is a reasonable chance of success but there is no guarantee that labour will result in a vaginal birth. The primary goal of labour is a healthy mother and healthy baby at the end. The secondary goal is to achieve a vaginal delivery if possible. Labour is unpredictable and attempting a vaginal birth after caesarean requires extra vigilance and response to circumstances as they arise.
The most concerning complication is when the scar from the caesarean section weakens and opens up during labour. Scar rupture occurs in less than one percent of labours after caesarean delivery. Scar rupture may have no consequence other than the need for repeat caesarean section or more rarely it can result in catastrophic events. If the scar ruptures during labour and the placenta is dislodged this can result in fetal death and severe bleeding requiring blood transfusion for the mother. If the uterus is severely damaged from scar rupture or excess bleeding cannot be controlled, then a hysterectomy may be required to save the life of the mother.
It is very important that any trial of labour has limits on duration and is well-monitored for signs of fetal compromise in a setting where immediate management is available. During active labour the fetal heart will be monitored continuously. Monitoring can occur wirelessly so that, with one belt around your abdomen, it is still possible to move around the room and even be in the shower. A fetal scalp electrode (fine wire the thickness of a hair placed into outer layer of fetal scalp at an internal examination) may be required for accurate monitoring. IV cannulation and collection of a blood count and group and hold will occur during early labour to save time if IV access is required.
If there are any suggestions that labour is not progressing well or any signs that baby is becoming distressed, then an emergency caesarean section will be performed as soon as possible. If there is slow progress or signs of fetal distress at fully dilated in the pushing stage then help to deliver vaginally with vacuum extraction or forceps can be given.
Almost always, emergency deliveries can be achieved before there are any problems for baby. There are tiny risks of hypoxic injury (lack of oxygen resulting in fetal death, cerebral palsy or short-term admission to special care nursery) or traumatic injury (superficial scalp injuries from vacuum extraction, facial injuries from forceps delivery, or arm or shoulder injuries from shoulder dystocia (tight or stuck shoulders)) at vaginal birth. These risks are similar for labour generally and apart from scar rupture are not specific to vaginal birth after caesarean section.
Vaginal birth may be associated with trauma to the perineum requiring repair and longer term there may be issues with pelvic floor weakness, urinary incontinence or altered bowel function. This is the same for all first vaginal births.
If labour occurred and some cervical dilatation was achieved prior to the previous caesarean section, then usually the first part of labour will be more efficient and cervical dilatation will occur more quickly, similar to someone who has laboured previously. Close observation of progress is still required to see that the cervix becomes fully dilated and the head descends low enough in the pelvis to achieve vaginal birth.
Labouring spontaneously without the need for induction is associated with a better chance of achieving vaginal birth after caesarean. Induction with prostaglandins or Syntocinon infusion after membrane rupture is associated with an increased chance of scar rupture. Induction can still be undertaken and may achieve vaginal birth after caesarean. Ripening of the closed cervix with a balloon catheter instead of using prostaglandins may be preferable. If contractions do not establish after spontaneous or assisted rupture of membranes, Syntocinon infusion can be used cautiously .As for all pregnancies, presentation to the Pregnancy Assessment Centre should occur if there are concerns about any reduction in baby’s movements, if membranes rupture (gushes or trickles of fluid vaginally), if there is vaginal bleeding like a period (more blood than mucus), if there is severe or constant abdominal pain or if there are regular contractions.
If the fetal head is high and the cervix is unfavourable for labour after the due date, then an elective repeat Lower Segment Caesarean Section may be preferable to a lengthy induction of labour. There are some possible complications associated with caesarean section. With any operation there is a risk of infection even though a dose of preventative antibiotics will be given during the procedure. Infection in the uterus, wound, bladder or breasts may require antibiotics in the postpartum period. Excess bleeding may require blood transfusion, additional medications and surgical procedures, including a remote chance of hysterectomy. Damage to bowel, bladder, ureter and blood vessels may require further surgery at the time of caesarean or shortly after. There is a low risk of clots in the legs and lungs and this will be reduced by wearing compression stockings and clexane injections.
A planned Lower Segment Caesarean Section prior to labour has less risk of complications than an emergency caesarean section during labour. In particular there are increased risks of infection, excessive bleeding and clots in the legs and lungs after an emergency caesarean section. Most caesarean sections are performed under spinal or epidural block. Less than 2% of emergency caesarean sections are performed under General Anaesthetic but this may be required in an emergency if there is not time to achieve an effective spinal or to top up an epidural block.
Other considerations prior to VBAC may be conditions where labour may be best avoided such as low-lying placenta, breech presentation, twin pregnancy or if there is suspected maternal or fetal compromise. If a previous caesarean section was performed for failure to progress in labour this may be due to pelvic dimensions being smaller than fetal head dimensions. While CT pelvimetry does not predict vaginal birth, measuring the bony pelvic dimensions after 36 weeks gestation can provide reassurance that these are not below the minimum required. An estimate of fetal size may be reassuring that fetal head circumference and fetal weight are not larger than in a previous unsuccessful labour. While a less than average pelvis or larger fetus do not preclude VBAC, more vigilance is required during labour for adequate progress of cervical dilatation and head descent. There is some evidence that there are more complications for VBAC, if the birth to birth interval after caesarean is less than 2 years. The scar on the uterus reaches full strength by 12 months after caesarean section so it is better to conceive at least 12 months after a caesarean if vaginal birth after caesarean is planned.