The Evidence on VBAC: Safety and Success Rates

chanelle campbell
Oct 29
5 min read

Black-and-white image of a newborn baby with outstretched arms following a successful VBAC (Vaginal Birth After Cesarean), representing empowerment, natural birth, and informed choices for mothers

Vaginal birth after cesarean (VBAC) is a valuable option for women with a prior cesarean delivery who are considering their choices for subsequent births [1][2]. This blog post aims to provide an evidence-based overview of VBAC, focusing on safety and success rates, to equip VBAC practitioners with the knowledge to support informed decision-making.

What is VBAC?

VBAC refers to delivering a baby vaginally after a previous delivery by cesarean section [1][3]. Attempting a VBAC involves a trial of labour after cesarean (TOLAC), where the woman labours with the goal of achieving a vaginal birth [3][4].

Historical Context

The saying "once a cesarean, always a cesarean" was a common belief in the past [5]. However, research has shown VBAC to be a safe and reasonable choice for many women, leading to a shift in this belief [5][6].

Benefits of VBAC

VBAC offers several potential benefits compared to repeat cesarean sections [4][7]:

Reduced Maternal Morbidity: Successful VBAC is associated with decreased maternal morbidity, such as blood transfusion, infection, and hysterectomy [7].
Fewer Complications in Future Pregnancies: VBAC can decrease the risk of complications like abnormal placental implantation (placenta previa/accreta), ectopic pregnancy, stillbirth, and preterm birth in subsequent pregnancies [1][2].
Avoidance of Surgery: VBAC avoids the risks associated with repeat surgeries, such as incision pain and wound infection [7].
Improved Postpartum Recovery: VBAC is often linked to earlier skin-to-skin contact, earlier breastfeeding initiation, shorter hospital stays, and easier recovery [7].
Decreased Overall Cesarean Delivery Rate: Increasing VBAC rates can contribute to a decrease in the overall cesarean delivery rate [1].

Success Rates of VBAC

The success rate of VBAC typically ranges from 60% to 80% [1][8]. Factors influencing VBAC success include [2][9]:

Prior Vaginal Birth: Women with a prior vaginal delivery, especially a prior successful VBAC, have a higher likelihood of VBAC success [2][5]. Success rates are even higher (85-90%) if there was a previous vaginal birth after a prior cesarean delivery [2][10].
Spontaneous Labour: Spontaneous onset of labour is associated with higher VBAC success rates [1][11].
Non-Recurring Indication for Prior Cesarean: If the reason for the first cesarean is not present in the subsequent pregnancy (e.g., breech presentation), the chances of VBAC success increase [5][12]. The overall proportion of successful VBAC is greater than 60% if the primary CS was done for non-recurring indications [12].
Inter-delivery Interval: An inter-delivery interval of more than 18-24 months from the primary CS may improve VBAC success and decrease the risk of uterine rupture [7][13].
Maternal Characteristics: Factors such as younger maternal age (<35 or <40 years), normal BMI, and being of Caucasian race are associated with successful VBAC [9][14]. Greater maternal height is also associated with increased likelihood of successful VBAC [10].
Favourable Cervical Examination: A favourable initial pelvic examination, consisting of cervical dilation >1 cm, cervical effacement >50% or station -1 or lower, is a good indicator of success [14]. Those admitted with cervical diameter greater than 3 cm (active first stage of labour) had a strong likelihood of vaginal delivery [14].
Infant Birthweight: Lower infant birthweight (less than 4 kg) is associated with an increased likelihood of successful VBAC [10][14].

Risks of VBAC

While VBAC is generally safe, it is associated with certain risks [4][15]:

Uterine Rupture: This is the most significant concern with VBAC, where the prior uterine scar can separate during labour [4][15]. The risk of uterine rupture with a low transverse incision is relatively low, ranging from 0.5% to 0.9% [10][15]. However, if it occurs, it can lead to severe maternal and neonatal complications [16]. Continuous fetal monitoring is recommended as changes in the fetal heart rate are key indicators of uterine rupture [1][17].
Need for Emergency Cesarean Delivery: 20% to 40% of planned VBAC attempts may end in the need for a cesarean section [7]. Emergency repeat cesareans carry greater risks than elective repeat cesareans [7][16].
Fetal Complications: Uterine rupture can interrupt oxygen supply to the baby, potentially leading to fetal acidosis, NICU admission, fetal asphyxia, or even death [16][18].

Contraindications to VBAC

Certain conditions make VBAC less safe [19][20]:

Prior classical or inverted T uterine scar [10][19].
Previous uterine rupture [19][20].
Placenta previa [10][21].
Transverse lie of the baby.
Prior hysterectomy or myomectomy entering the uterine cavity [2][21].

VBAC after two Cesarean Sections (VBAC-2)

Women with two prior low-transverse cesarean incisions may be candidates for VBAC and should be counselled based on the factors that affect their likelihood of vaginal birth [2][22]. Labour should be conducted in a centre with suitable expertise and recourse to immediate surgical delivery [2].

The Role of Practitioners

VBAC practitioners play a crucial role in [23][24]:

Counselling: Providing comprehensive counselling to women considering VBAC, discussing the risks, benefits, and alternatives [1][21]. The antenatal counselling process should be documented in the medical records [21].
Patient Selection: Identifying suitable candidates for VBAC based on their medical history and individual circumstances [1][21].
Monitoring: Closely monitoring the mother and baby during labour, with continuous fetal heart rate monitoring [1][17].
Emergency Preparedness: Ensuring that the facility is equipped for emergency cesarean delivery if needed [1][19].

Conclusion

VBAC is a safe and valid option for many women with a prior cesarean delivery [1][6]. By understanding the evidence-based information on safety and success rates, VBAC practitioners can empower women to make informed decisions and provide them with the best possible care [23][24].