In countries such as Australia, the UK and the US, around 1 in 3 women have their baby via c-section. This means a significant amount of women are going into their next labour with a uterine scar. Uterine rupture is the main risk which concerns women who are planning a VBAC, and the main reason their care providers place limitations around the way and length of time they can labour (called a ‘trial of labour’).
It can be challenging to sift through the available information to find the facts about uterine rupture and how it might impact your labour and birth.
What is a uterine rupture?
A uterine rupture occurs when the scar opens completely along its length and through all three layers of the uterus. The amniotic sac surrounding the baby ruptures and the baby or placenta can be pushed through the rupture and into the abdominal cavity.
When a scar ruptures through all of the uterine layers, it is referred to as a complete or catastrophic rupture. It’s a rare complication but does have the potential to be very serious for both mother and baby. It requires a c-section immediately.
When a scar only stretches or partially opens, this is referred to as a ‘window’ or uterine dehiscence. The existing scar tissue stretches, and the underlying two layers may separate, but the outer layer of the uterus (perimetrium) remains intact.
This can also be called a silent or incomplete rupture, which is misleading, as the scar has not opened completely, but only thinned or partially separated. Scar dehiscence is a common event, and rarely has any risks for mother or baby.
Signs of uterine rupture
A uterine scar rupture cannot be predicted before it happens, only diagnosed as it actually occurs. There are studies that suggest measuring the thickness of the scar by ultrasound, or following closely the pattern of contractions in labour may indicate if a rupture is likely to occur. But there is not enough information available to indicate if these methods are accurate enough to be widely adopted.
Uterine rupture usually has the following signs:
- Excessive vaginal bleeding
- Sharp pain between contractions and/or sharp pain at the scar site
- Contractions that slow down or become less intense
- Unusual abdominal pain or tenderness
- Baby’s head moving back up not down the birth canal
- Baby’s head is bulging under the pubic bone, indicating the head is outside the uterus
- The uterus loses muscle tone (uterine atony)
- Rapid heart rate and abnormally low blood pressure in the mother
- Baby’s heart tones are abnormal, variable or slow.
What are the risk factors for uterine rupture?
There is no way to predict which women are more likely to experience uterine scar rupture during a VBAC.
However, studies have shown the risks are reduced if:
- Labour begins on its own (no induction of labour) and continues without augmentation. There is an increased risk of uterine rupture and c-section in induced and augmented labours compared with spontaneous labours
- Your due date is at least 18 months after your previous c-section
- Previous c-section incision was low-transverse (horizontal incision made in the lower part of the uterus).
- A previous successful VBAC
- Previous c-section was performed for reasons other than obstructed labour (such as placenta previa or breech presentation) and is unlikely to be repeated.
- You have only one previous c-section
- Your doctor used a double layer suture rather than a single layer to close the incision for your previous surgery.
Many studies report that women who’ve had one previous c-section and have a low-transverse scar, the risk of uterine rupture is less than 1%.
What are the complications of uterine scar rupture?
Uterine rupture is rarely life-threatening for the birthing woman, although there are risks associated with c-section surgery.
Rarely, mothers will require blood transfusions or even a hysterectomy if the blood loss is excessive, or the tear cannot be repaired.
While a uterine scar rupture during VBAC labour is rare, the consequences for the baby are serious. The immediate medical response is an emergency c-section.
If there is a lapse of time in diagnosing and responding to a uterine rupture, there is a greater risk of the baby/or placenta being pushed through the uterine wall and into the mother’s abdominal cavity. This increases the chances of the mother haemorrhaging, and the baby is more likely to be deprived of oxygen, causing brain damage and death.
The loss of the baby occurs in less than 6% of all uterine ruptures. As uterine scar rupture is itself a rare event, occurring in less than 1% of VBAC labours, the overall risk of losing a baby due to uterine rupture is extremely low. You are more likely to experience a cord prolapse or placental abruption during a VBAC labour than uterine rupture. Babies are more at risk of dying from those rare complications than of uterine scar rupture.
What puts me at high risk of scar rupture?
There are rare situations when your risk of scar rupture is greater if you attempt labour after a c-section. These risk factors are believed to affect about 10 out of every 100 women:
- The previous c-section was a classic or T-shaped incision. Classic incisions are vertical cuts made in the upper part of the uterus. T-shaped (or inverted T) are incisions that involve a vertical and horizontal cut. The risk of rupture for these scars has been reported to be between 4% and 9%.
- Previous uterine surgery for reproductive or gynaecologic problems
- Ultrasound during late pregnancy may detect the scar area has thinned to less than 2.5 millimetres
- During a previous labour a uterine scar has ruptured.
It important that women planning a VBAC have access to evidence based information and the support of their care provider in order to make the best decision for their personal circumstances. Most women have a good chance of success for a VBAC and should choose care providers who are trained and experienced in attending VBAC births in order to maximise their chances of a successful birth outcome.