Mechanical Dilation of the Cervix in a Scarred Uterus

To determine if mechanical labour induction can offer a safer and effective alternative to prostaglandins to women with previous caesarean section attempting trial of labour after caesarean (TOLAC).

There is good evidence to show that induction of labour with a transcervical balloon compares favourably with the use of prostaglandins.The cervical balloon works by softening \& stretching the cervix mechanically \& stimulates the release of endogenous prostaglandins.

When compared with prostaglandins, meta-analysis have shown that for TCB induction, there is no significant different in caesarean section rates (27% vs 25%) with a reduced risk of hyperstimulation with fetal heart rate change (0.4% vs 3%). Further, when compared against induction with misoprostol, induction with a Foley catheter balloon was found to have a lower rate of caesarean section for a non-reassuring fetal heart rate (RR 0.54, 95% CI 0.37-0.79) and a fewer vaginal instrumental deliveries (RR 0.74, 95% CI 0.55-0.95) \[41\]. One randomized controlled trial of 824 women with no previous caesarean section comparing foley catheter balloon with a prostaglandin E2 gel demonstrated no difference in caesarean section rates \& 2 cases of uterine rupture or perforation in the prostaglandin E2 arm but not in the foley catheter balloon arm. Another study involving 1859 women comparing foley catheter balloon with oral misoprostol showed no difference in caesarean section rates or complications. It was, however, noted that induction with foley catheter balloon more likely required oxytocin induction at 80.3% vs 68.4% for misoprostol.

While there were earlier concerns of an increase in infectious morbidity when using mechanical induction of labour due to the presence of a foreign body, more recent RCTs \& meta-analysis have shown that there is no significant increase.

One of the main concerns for induction of labour in patients with a previous uterine scar is an increased risk of uterine rupture. One observational study of 20,095 women quoted a risk of uterine rupture in spontaneous labour to be 0.52% \& in prostaglandin-induced labour to be 0.77%. Another observational study involving 33,699 women quoted a risk of 0.4% and 1% respectively. While there are also studies which suggest that there is no significant increase in the rate of uterine rupture, many professional bodies have discouraged prostaglandin-induction in women with previous scars.

Due to lower levels of hyperstimulation that could lead to fetal distress or uterine rupture, trans cervical balloon induction has found itself as a possible, safer means of induction of labour for women who are keen for vaginal birth after caesarean and are agreeable with induction. Most RCTs were small in size \& did not demonstrate any uterine rupture or dehiscence. However, 2 retrospective cohort studies involving a size of 2479 \& 208 women respectively showed a uterine rupture rate of about 0.5%. trans cervical balloon induction appears to be a safe method for inducing consenting women keen for vaginal birth after caesarean and this study will contribute towards this body of evidence.

Eligibility Criteria:
Inclusion Criteria:

* Female ≥ 21 years of age at booking visit
* 1 previous uncomplicated lower segment caesarean section (CS)
* Aiming for TOLAC
* Written informed consent (and assent when applicable) obtained from subject or subject's legal representative and ability for subject to comply with the requirements of the study
* Singleton pregnancy
* Gestational age \>37 weeks
* Understands risk of TOLAC
* Eligible for induction of labour for the standard obstetric indications, including post-date or post-term pregnancies at 40-41 completed weeks of gestation
* Unfavourable Bishop's Score ≤ 5 requiring cervical priming
* Previous uterine surgery, including simple myomectomy, where there is no contraindication to TOLAC
* Reactive CTG pre-induction
* Ruptured membranes

Exclusion Criteria:

* Refusal to participate
* Women with 2 or more previous CS
* Previous classical or lower segment vertical incision, or inverted T or J incision in the previous caesarean delivery
* Previous uterine surgery with contra-indication to future TOLAC
* Maternal contraindication for vaginal delivery
* Fetal contraindication for vaginal delivery or major fetal abnormality
* Malpresentation or cord presentation
* Placenta praevia \<20mm from internal os
* Chorioamnionitis
* Antepartum haemorrhage of undetermined origin AND deemed a contraindication for TOLAC
* Suspected fetal macrosomia (estimated weight on ultrasound \>4kg) AND deemed a contraindication for TOLAC
* Congenital uterine abnormality
* Multifetal pregnancy
* Latex allergy or poorly-controlled asthma