**5. VBAC predictive factors**

The success rate of planned VBAC has been quoted to be between 75 and 90% [22] and consensus from evidence-based guidelines and systematic reviews have endorsed

VBAC as a safe alternative for delivery for majority women with prior single lower segment CD, with a complication risk of less than 1% [14, 21–23]. Therefore, there is a need during prenatal care to carefully select women, counsel them appropriately and implement a VBAC checklist which will improve success and prevent complication and litigation [21, 22, 30]. Several factors have been found to positively predict successful VBAC and this should be carefully assessed during the entire prenatal care. Evidence based research has established the followings factors to impact positively on the success of VBAC:

## **5.1 Maternal will**

Prospective parturient(s) who are well motivated to have VBAC after careful selection and counselling is associated with a positive outcome and higher chances of successful VBAC. This has been found to be critical in patients that undergo VBAC when compared to patients that are unwilling to try a vaginal delivery [21, 22, 31, 32].

#### **5.2 Body Mass index < 30 kg/M2**

VBAC success rate is inversely proportional to increasing BMI. VBAC rate decreases in obese women, however, appears unchanged in overweight women [33]. Weight fluctuation between pregnancy is correlated with decrease VBAC rates especially among women who had normal BMI in previous pregnancy [32].

### **5.3 Single previous lower segment caesarean delivery**

The risk of uterine rupture associated with a single uncomplicated lower segment caesarean section is very rare. The likelihood of uterine rupture is approximately one in 200 (0.5%) women [21, 22]. Caution should be exercised in women who have had a complicated lower segment caesarean section despite insufficient data on extension or inverted T or a J incision. Recommended mode of delivery in these women should be decided on case-by-case basis with the woman fully aware of risk of uncertainty [21, 22, 33]. Previous classical uterine incision is associated with a higher risk (5% or greater) of uterine rupture; therefore, this incision type and previous uterine rupture are absolute contraindications to VBAC, and all such women should be offered elective repeat caesarean section [21, 34–36]. There is conflicting evidence on the likelihood of uterine rupture on women with two previous lower segment caesarean sections. Women with two previous uncomplicated lower segment caesarean deliveries have VBAC success rates of 62–75% which is like single lower segment caesarean sections especially among women with previous vaginal delivery or previous successful VBAC [32]. However, it is reasonable to err on the side of caution and offer such women elective repeat caesarean section due to the conflicting data.

#### **5.4 Non recurrent indication for CS**

Indication of the previous caesarean section can influence the outcome of VBAC. Non recurrent indications are associated with higher rates of successful VBAC. Sixty percent of women with cephalopelvic disproportion as the indication for previous caesarean delivery will achieve vaginal delivery, while 89% will achieve vaginal delivery for non-recurrent indications [32].

### **5.5 Previous successful vaginal birth before or after VBAC**

Prior vaginal delivery is the strongest positive predictor of VBAC. VBAC Success rate in women with a prior vaginal delivery is documented to range between 75 and 85%, while a prior successful VBAC gives the maximum success rate of between 90 and 93% [21–23, 32, 37].

#### **5.6 Adequate inter pregnancy or inter delivery interval**

The hysterotomy exact mechanism of healing is still blur regeneration and fibrosis both entertained. According to Buhimschi et al. [38], the healing and visco-elastic behaviour of a surgically wounded myometrium depends on and varies with genetic and phenotypic properties. According to the CORONIS multicentered 3 year follow up randomised control trial, uterine rupture and uterine scar dehiscence following a single or double layer closure were similar in patient that had TOLAC [39]. Therefore, in a case to standardised caesarean section a single layer closure of the uterus is recommended [40]. The recommended optimal interval to guaranty uterine scar integrity and to reduce the risk of uterine is 6 and 18 months for interpregnancy and Interdelivery intervals respectively [27, 32]. However, a recent retrospective study recommended an Interdelivery interval of 24 months to attempt VBAC [26].

#### **5.7 Singleton and cephalic presentation considered favourable for VBAC**

There is high success rate in women attempting VBAC with a singleton fetus in cephalic presentation with estimated fetal weight of less than 4000 g, although there are studies to demonstrate that women undergoing TOLAC with one prior low transverse caesarean delivery with twin gestation have similar outcomes [21–23, 32]. TOLAC in twin gestation with no prior vaginal delivery is associated with very low successful VBAC rate following evidence from a recent cohort report [41]. However, the Royal College of Obstetricians and Gynaecologist threshold for estimated fetal weight is 3800 g [22].

#### **5.8 Spontaneous onset of labor has better prognosis for VBAC**

Spontaneous onset of labour in a woman who is planned for VBAC has been associated with higher success rates and less complications compared with artificial initiation or augmentation of uterine contractions. In a recent metaanalysis of observational studies oxytocin use was associated with higher rate of uterine rupture and recommended cautious monitoring of oxytocin use during TOLAC [42].

### **6. VBAC check list**

A VBAC check list will enable obstetricians and physicians in women's health to carefully select patients, improve communications, and avoid litigation from possible acts of omission and lack of proper documentation (**Table 1**). Below is an example of Queensland Clinical Guideline for Vaginal birth after caesarean (VBAC) which was adopted by Royal College of Obstetricians and Gynaecologists (**Table 2**) [21, 22].


#### **Table 1.**

*Queensland Clinical Guideline Vaginal birth after caesarean (VBAC) which was adopted by Royal College of Obstetricians and Gynaecologists (RCOG) [21, 22].*
