This muscle plays a major role in childbirth. It has to open up for the baby to pass through, has to stretch by a 200-1000%, depending on how elastic it is which varies a lot between people. We already know that a more elastic muscle means a shorter 2nd stage of labour.

In Video 1 you can see that the puborectalis muscle, a V shaped structure which is about as thick as a finger, is anchored to the bone at the top. The view is from the bottom up, as if looking at the pelvic floor from below. The left hand image is the patient’s right side, the top of the image is the pubic bone, and the bottom of the image is close to the end of the spine. Vagina, urethra and back passage fill the space inside the V and have been digitally ‘removed’.

On playing the video you can see that the V of the muscle gets wider higher up, that is, further up the vagina.  The area that is most likely to suffer in childbirth is the thickest, lowermost part, because it has to stretch most, and fastest (during crowning of the head).

Normally, skeletal muscle (the kind we usually mean when we talk of muscle) can’t stretch to more than twice its length without tearing. The puborectalis muscle often has to stretch by much more. The miracle is that in many women it doesn’t tear and even returns to normal after letting the baby through. Nobody understands how this is possible, but we assume it has something to do with hormonal effects of pregnancy.

However, it happens often enough that the muscle does tear, something that was first shown in 1943, only to be forgotten for 60 years. It’s incredible but true. We can sometimes even see the damage in labour ward, in women who have vaginal tears. It’s just that nobody ever looked for damage to the underlying muscle, and nobody seems to ever have tried to fix it, until 2007!

Commonly, the puborectalis muscle comes off the bone of the pelvic sidewall during crowning of the baby’s head. This happens at the last minute, when the baby’s head is just visible in the vagina. Women who need a Caesarean Section in labour, regard-less of the timing, never have this kind of pelvic floor damage.

Over the last few years we have learned how to detect tears of the muscle, not just at birth, but also much later, with magnetic resonance imaging and ultrasound, and even by just using our fingers. A 4D pelvic floor ultrasound shows the entire pelvic floor in realtime, and we can see what happens when someone pushes or bears down, stretching the muscle (see Video 2).

In some women, even some who have never given birth the normal way, this muscle stretches a lot (see Figure 1) on pushing or just coughing. This is probably good for having babies, but it means a higher risk of prolapse of the womb, bladder and back passage. These conditions mean that someone feels a lump in the vagina that may even stick out, and there can also be bladder symptoms or problems with the back passage.

Childbirth means that this muscle has to stretch a lot. Sometimes it’s already very stretchy even before childbirth, probably due to genetic factors, and sometimes it is stiff before and is overstretched, not coming back to normal afterwards. And sometimes it simply tears off the pelvic sidewall.

Whether someone suffers damage to this muscle in labour or not seems to depend on many things. The older a woman is when she has her first baby, the more likely is trauma to the pelvic floor (see Figure 2). That’s very important. People should know about this when they think about having kids. The longer one waits with having children, the lower the likelihood of falling pregnant without help, and the higher the risk of needing a Caesarean or Vacuum or Forceps. And even if a woman manages to avoid a Caesarean, the risk of pelvic floor muscle trauma rises by about 10% with every year of delay in having your first child. Incidentally, it’s the first baby that matters the most. Whether someone has one child born the normal way or three doesn’t seem to make much of a difference to the pelvic floor. A second baby does not seem to cause much additional damage- unless the first was born by Caesarean, and the second the normal way.

The more difficult a vaginal delivery, the higher the risk of pelvic floor injury.  and other factors such as a long labour and a big baby probably increase the risk as well. There are studies from all over the world showing that Forceps triples the risk of pelvic floor muscle tears. Rotational Forceps is particularly bad. Other factors such as a big baby and a long second stage may also make damage more likely, but an Epidural seems to protect the pelvic floor to some degree.

Figure 3-5 show what this damage looks like on magnetic resonance and ultrasound imaging in a woman three months after a normal delivery. So far, nobody has been able to repair this kind of damage. Immediately after childbirth the muscle is over-stretched and thin, and stitches seem to simply come loose soon after the repair. There may be other ways of fixing the damage, or just of compensating for it, but such research is still in the initial stages.

Some childbirth-related damage, such as small perineal tears, are often not repaired because we think they’ll heal well by themselves. So, do those pelvic floor muscle tears heal?

Once the muscle is pulled off the bone it shrinks and pulls back towards the back passage (it ‘retracts’), and there is no way it can move back to where it came from. In some women the tears are not complete, and scar tissue can bridge a partial tear, but that’s not the 15-25% of women we’re talking about here. Once the muscle is off the bone, the defect probably won’t heal. And in some women this happens on both sides, making matters worse (see Video 3).

Do defects of the pelvic floor muscle (‘avulsions’) matter? After all, Obstetricians and Gynaecologists seem to have completely missed them until now!

Well, there surely are many thousands of women in the community who have suffered this kind of trauma in childbirth, without noticing any problems. Partly this may be due to the fact that such problems sometimes take a long time to develop, but in others those parts of the pelvic floor muscle that are higher up (mainly the iliococcygeus muscle) can compensate and take most of the load of the pelvic organs.

All we can say right now is that pelvic floor muscle trauma (‘avulsion’)

-weakens the muscle by about 1/3 on average

-makes the muscle more stretchy by about 50%

-enlarges the opening of the pelvic floor (the ‘hiatus’) by about 1/4

-more than doubles the risk of bladder prolapse

-triples the risk of prolapse of the uterus (the womb).

-triples the risk of a prolapse returning after pelvic floor surgery.

The link with loss of urine on coughing sneezing etc (something people often blame on a ‘weak pelvic floor’) is much less obvious. Urine leakage is a little more common in women with a damaged pelvic floor, but there are many other factors involved.

And then there is another question: how much does over- stretching or tearing of this muscle affect sexual function? In some women the site of the tear is very tender, even after decades, and some women and their partners notice a big difference after the birth of their first child. Others don’t notice anything. On average, women feel that there is more laxity and less muscle strength in the vagina, and sometimes that makes them seek help from gynaecologists who end up suggesting some kind of vaginal surgery, unaware of what the real problem is.

Overall we can say that trauma to the pelvic floor muscle has a marked negative effect on pelvic floor structure and function. It’s probably responsible for many (if not most) cases of prolapse of the womb and bladder.

This surely means that we ought to work out how to predict and prevent such trauma, and how to fix it once it’s happened. Most of the research we’re doing at my unit revolves around those issues. While it is possible to reconnect an avulsed puborectalis muscle, this seems to have limited effect. The muscle probably often is not just torn, but also overstretched, and fixing that may need other approaches that focus on reducing the size of the levator hiatus rather than just repairing avulsion trauma. We have done about 100 procedures to reduce the size of the opening in the pelvic floor (the ‘levator hiatus’), and on average we can reduce it by 1/4 to 1/3, but it’s not yet proven that this stops prolapse from coming back. We’ll test this technique (the ‘puborectalis sling’) further in a larger study about to start at six different hospitals in NSW, Queensland, Victoria and South Australia.

It’s even more important to prevent this kind of damage in the first instance. We have an ongoing study at two hospitals in Sydney where we use a commer-cially available device, the ‘EpiNo’, to try and prevent pelvic floor damage. Results from our pilot study in 200 women look very promising. The main study is still ongoing, with 540 women recruited so far, and should be complete in 2014.


General information for non- Health Professionals

The topic of pelvic floor damage in childbirth is attracting more and more attention from non-medical people. This is not surprising- after all, most women who have given birth naturally, are affected, and so are their partners. Until recently we thought that ‘pelvic floor trauma’ meant perineal and vaginal tears, and damage to the anal sphincter, the muscle that surrounds the end of the back passage. In developing countries especially this includes fistulae, that is, abnormal connections between vagina and bladder (vesicovaginal fistula) or back passage (rectovaginal fistula), but these are uncommon in developed countries with good medical care.

We now know that ‘pelvic floor trauma’ is much more than what we’ve been taught to stitch in labour ward. In 15-25% of all women who have given birth normally there is serious damage to the pelvic floor muscle, the ‘puborectalis muscle’. This is a very recent discovery and not yet in most textbooks, so don’t be surprised if it’s news to your healthcare provider.

Video 1: This is what the pelvic floor muscle looks like normally, seen from below.

Figure 2: The relationship between age of the mother at her first delivery and pelvic floor muscle trauma (from: Dietz and Simpson, ANZJOG 2007; 491-495).

Video 2: Pelvic floor ultrasound during bearing down. This is a thick, healthy muscle that doesn’t stretch much.

Figure 3: Right- sided tear of the puborectalis muscle (indicated by star) on MR (left) and 3D ultrasound (right), seen 3 months after a normal delivery.

Video 3: Severe over-stretching of the pelvic floor muscle in a patient with bilateral pelvic floor muscle tears. The effect is most visible on the bottom right image.

Figure 5: Bilateral tear of the puborectalis muscle (indicated by stars) on MR (left) and 3D ultrasound (right), seen 6 months after a Vacuum delivery.

Figure 1: This is how much the elasticity of the pelvic floor muscle can vary from one person to the next.

Figure 4: Left- sided tear of the puborectalis muscle on tomographic 3D ultrasound. The defect is about 1.5 cm wide.