If you're planning a VBAC, you've probably heard about uterine scar rupture. But you've unlikely heard of uterine dehiscence. This article has been written to help you understand what it means and what you need to be aware of.
Today, around one-third of women are giving birth by c-section.
While these women may know there are risks for the surgery itself, they may be unaware that having a c-section can increase their risk for a number of complications in their next pregnancy and birth.
The number one risk factor cited as being a negative reason for a planned vaginal birth after c-section (VBAC) is uterine scar rupture.
A uterine scar rupture occurs when the scar opens completely along its length, and through all layers of the uterus. This is usually referred to as a complete or catastrophic rupture. The amniotic sac surrounding the baby ruptures and the baby or placenta can be pushed through the rupture and into the abdominal cavity.
It is a rare complication occurring in under 1% of all VBAC labours, and has the potential to be very serious for both mother and baby, requiring an immediate c-section.
What many women are not aware of is the term ‘uterine rupture’ is often used to describe more than one event involving c-section scars. The first event is called a ‘window’ and is the thinning of scar tissue, to the point it is see through. The second is a dehiscence, which happens when the scar tissue begins to separate a small amount.
What is Scar Tissue?
In order to understand uterine scar integrity it is important to understand what scar tissue is. When the tissue in our bodies is damaged, scar tissue forms as part of the normal healing process. After a c-section scar tissue forms on the external skin area as well as internally along the incision made in the uterus.
Our skeletal tissue is made of collagen, formed in a particular way to allow for flexibility and function. When scar tissue forms, our body produces excessive amounts of collagen, but it is doesn’t have the same structure or flexibility as the tissue it is replacing. It is stronger but not as functional as our normal tissue.
Separation Versus Rupture – What Is The Difference?
The uterus has three layers: the inner lining (endometrium); the middle muscular layer (myometrium); and the outer layer (perimetrium).
When a c-setion is performed, the surgeon must cut through the three layers of the uterus to reach the baby (the rectus abdominal muscles are not cut but moved aside). When the surgery is completed, the uterus is sutured closed and within a few weeks scar tissue has formed.
During your next pregnancy the scar tissue stretches as your uterus grows to accommodate your growing baby. Most of the time the scar holds together and you would not be aware of what is happening underneath your skin. If a c-section is performed and the area is paper thin or see-through, it is referred to as a ‘window’ or ‘markedly thin’ scar.
It isn’t clear if a markedly thin scar is a risk for further separation or rupture. Unless the scar area is being monitored by ultrasound or a c-section is performed, women go on to successfully VBAC without being aware their scar has thinned but is holding together as it should. If a c-section is performed doctors may assume this means the scar was about to separate but there is no clear evidence that this is the natural progression of scar tissue becoming thin.
If the scar partially opens, much like a zip coming open a little way, this is referred to as a uterine dehiscence. The existing scar tissue stretches and the lower layer separates, but the outer layer of the uterus (perimetrium) remains intact. There may be some or no bleeding and if it happens during pregnancy the scar opening can close again and heal over.
Sometimes a uterine dehiscence is called an ‘asymptomatic’ rupture because there are no or very mild symptoms to indicate the separation is happening. This terminology is misleading as scar dehiscence is mostly harmless and doesn’t affect mother or baby. The amniotic sac remains intact and the placenta and baby do not move outside the uterus into the abdominal cavity.
Does A Dehiscene Mean A Rupture Is Likely?
While uterine dehiscence has the potential to go on to become a rupture, again it is not clear at what point the scar will continue to hold or further separate. Monitoring the mother’s pulse rate carefully and consistently during labour is often the only sign that uterine dehiscence may be occurring. When the scar begins to separate a type of fluid that fills the body cavities leaks onto the membrane that separates abdominal organs from the cavity wall. When this occurs, the body’s shock response will dramatically increase the mother’s heart rate.
In a ten year Canadian study, dehiscence occurred at the same frequency as complete uterine rupture (2.4 in 1000 women). Overall scar dehiscence is believed to occur in around 1.1% of VBAC labours and complete scar rupture occurs in between 0.3 to 0.7% of VBAC labours.
If scar dehiscence occurs it is only noticed when a repeat c-section is performed for reasons other than uterine rupture (such as fetal distress or failure to progress). In the past doctors would manually explore the uterus after VBAC for tears but this practice is no longer routine as it increases pain and infection. Many scar dehiscence pass unnoticed if the mother has a successful VBAC, as there is generally no sign that a scar separation has occurred.
While VBAC should be an option for women who have low transverse c-section scars, it can still be a challenge to find a care provider who supports VBAC. Being aware of the differences between uterine dehiscence and scar rupture could mean the difference between achieving your VBAC and having a repeat c-section.