Vaginal birth after caesarean: what does the research say?

The caesarean rates for women who had given birth multiple times with a previous caesarean decreased slightly between 2003 (64.4%) and 2010 (64%) [2]. In 2010, in France, among women with a previous caesarean, 36% gave birth vaginally and 64% gave birth by caesarean [3].

If the causes of your caesarean section are not permanent (for example, if it is not an irreversible anatomical issue such as a pelvis that is too narrow), there is no reason not to try to give birth vaginally. If you attempt a VBAC, you have approximately a 70% chance of delivering vaginally, and approximately a 30% chance of having a caesarean section during labour. This holds true for a vaginal birth after one caesarean as well as after two caesareans [4]. 

The benefit of VBAC is that it is associated with a lower risk of maternal morbidity and fewer complications for mothers in subsequent pregnancies [5].

According to the results of recent studies, the related factors affecting the success of VBAC are [6]:

• A maternal age under 40
• A normal body mass index
• A gestational age of 40 weeks or less
• A birth interval of two years or more

Furthermore, less than 2/5 of the foetal head palpable abdominally, a station below -2 (foetal head position), a cervical dilation of 4 cm or more, and an active phase of labour lasting 7 hours or less would be significantly associated with successful VBAC [7].

The Haute Autorité de Santé (HAS) has published best practice guidelines on the indications for planned caesarean section, recommending vaginal birth after a single caesarean (except in cases of a corporeal scar) and permitting it after two caesareans. However, from three caesareans onwards, it recommends a planned caesarean section [8].

VBAC may be contraindicated in the following cases [9]:

A previous high vertical uterine incision (caesarean with an incision between the bikini line and the navel),

A classical uterine scar (the hysterotomy was performed on the body of the uterus),

A previous uterine rupture, in which the caesarean scar on the uterus opens, 

Certain types of previous uterine surgery, such as fibroid removal, 

Being pregnant with triplets or more, 

Placenta praevia, 

A baby in a transverse position, 

Having already had 3 caesarean sections.

An American study of nearly 26,000 pregnancies found a rate of uterine rupture and dehiscence of 0.08%, regardless of the mode of delivery [13]. 

In general, the literature reports a rate of below 0.5% in pregnancies following a caesarean section. For example, one study found rates of 0.24% for dehiscence and 0.24% for rupture following a caesarean [14]. In the case of a single uterine scar, the rate of uterine rupture falls between 0.1 and 0.5% [15]. 

These rates apply only to hospital births; there is very little data on more "natural" births. One study on VBACs in midwife-led units found a rupture rate of just 0.2% [16].

Women with classical vertical and low uterine scars have an increased risk of rupture compared to women who had a low transverse uterine incision at the time of their caesarean section. [20]

To find out more on this topic, see our article: caesarean scar. 

There are various forms of gel induction, and primarily two hormones are used: dinoprostone, also known as PG2, and misoprostol. Misoprostol appears to be associated with a tenfold increase in risk [21]. It should be noted that gel induction is rare in France.

For example, one study shows a 4.6-fold increase in risk [22]. However, another study does not show a significant increase in this risk (0.74% instead of 0.45%) [23]. Recommendations across different countries do not point towards a strict prohibition of labour induction, but do call for caution and increased monitoring.

The risk of rupture is approximately 3 times higher in the group of mothers over 30 than in the group of mothers under 30 [24].

Having previously given birth vaginally reduces the risk:

The risk of rupture is 2.5 to 5 times lower, depending on the studies, in the group of mothers who have previously given birth vaginally, compared with the group of mothers who have never given birth vaginally [25].  

Waiting long enough between pregnancies reduces the risk:
After 24 months, the risk of rupture is 2.5 times lower than in the group of VBACs attempted before 24 months [26].

Having a spontaneous labour reduces the risk:

The risk of rupture in women at term whose labour is induced is higher (1.5%) than the risk of rupture when labour begins spontaneously (0.8%) [27].

One argument is that, since VBAC carries a risk of life-threatening emergency caesarean (severe uterine rupture requiring rapid delivery of the baby), it is essential to place an epidural at the start of labour so that, if needed, a caesarean can be performed under epidural anaesthesia rather than general anaesthesia, which carries greater risks for the mother.

The other school of thought holds that in order to perform a caesarean section under epidural, the anaesthetic always needs to be topped up via the epidural, which takes a few minutes to take effect. A spinal anaesthetic could therefore be placed at the same time: if there is not enough time to place a spinal, there would likewise not have been enough time to top up the epidural, meaning the situation would represent a genuine indication for caesarean section under general anaesthetic. Insisting on an epidural would therefore serve no purpose, and it would be possible togive birth without an epidural.

A large observational study across 19 medical centres examined 30,132 non-labour caesarean sections in mothers who had undergone one or more caesareans. The researchers identified an increased risk of complications with the number of caesareans (need for transfusions, hysterectomy, placenta accreta) [33].

A placenta praevia is inserted on the lower segment of the uterus. One study found a 1.5 times higher risk of placenta praevia in patients who had undergone one caesarean section, a 2.5 times higher risk in patients who had undergone multiple caesarean sections, and a 35 times higher risk of placenta accreta in mothers with a placenta praevia who had previously had a caesarean section [34].

Placenta accreta is a placenta that is abnormally firmly attached to the uterus. 

Having had a caesarean section and a placenta praevia in a previous pregnancy significantly increases the risk of placenta accreta. At the time of delivery, the placenta will not detach easily, which can cause severe haemorrhage requiring either ligation of the arteries supplying the uterus or its removal, in which case having further children will no longer be possible.