Urogenital Hiatus is not another term for Spring Break

Someone sent me this article, Vaginal Birth Tied to Pelvic Muscle Weakness,  perhaps to see if I would poke a fork into my eye. I didn’t. I decided to write this instead.

But first, some fun facts:

Did you know that the average diameter of the molded fetal head is 9 cm? Even the cranium of the soon-to-be-big-headed baby folds up (neat!) into something that is 20% less than actual diameter length while in the birthing tube.

This is a “9 centimeter” model (not to scale):

Did you know, the average urogenital hiatus, before pushing out le bebe, is 2.5 cm.

This is 2.5 centimeters (also not to scale):

Urogenital hiatus sounds like one is taking a break from the genitalia of France, Germany, and Sweden, but it’s just a fancy word for the space created by the pelvic tissues making up genital canal — or, when you’re birthing,  the tube of descent.

If you divide 2.5 by 9, (or wait, is it 9 by 2.5?) our levator ani (see the pelvic model below) ends up with the stretch ratio of 3.54. Meaning this tissue lengthens 3.5 times its resting length in order to let the baby through.

On a side-(but-kind-of-related)-note: These are the pants I wore through both my pregnancies, during which my waist went from approximately 28 inches to 3500 inches. That’s a stretch ratio of a billion and something.

Here’s a closer image.

And an even better image.

In addition to being an excellent speller, I am a fantastic photographer.

As you can see, the amount of stretch placed on the material exceeded the abilities of the elastic, which caused the elastic to break down.

Even though skeletal muscle is elastic like the pants, muscle can only stretch so much before failing. You don’t have to worry about the vaginal muscle failing though, because it appears that the vaginal tissue can handle the load under natural circumstances.

Which brings me to the article.

I went and found the research the article was referencing. Which wasn’t easy because journalists never remember include the title of the article (grrrrr), which makes it a bit tough to find. In the end, I actually found two articles by the same author looking at the same group of women over a long period of time.

So here’s the deal. While the internet article reads Vaginal Birth Tied to Pelvic Muscle Weakness, it should really read Operative Vaginal Birth Tied to Pelvic Muscle Weakness. Yes, women who had c-sections had “stronger” pelvic floors then those who delivered vaginally. But when the type of vaginal delivery was considered (i.e. were there any interventions like forceps, or episiotomy, or vacuums), it turns out that vaginal delivery wasn’t the issue. The greatest association was between pelvic floor disorder and Operative Vaginal Birth not Spontaneous Vaginal Delivery.

Why? In an object-free delivery the pelvic tissues are already stretching to maximum capacity. So that little *extra* stretch for forceps and their movements, you can see how one can easily exceed the tissue’s limit and leave them stretched beyond the point of no return. Just like my pants.

Which reminds me, I need new pants.

But some of the good news from the other article is this: Pelvic floor “strength” is not necessarily associated with pelvic floor disorder. In fact, in this study, the cesarean group with the most Pelvic Organ Prolapse had the “strongest” pelvic floors. Which means a much much better title for the article should be Operative Vaginal Birth Tied to Pelvic Muscle Weakness, but Pelvic Muscle Weakness not Tied to Pelvic Floor Disorder and Tied Much More to Operative Intervention.

And one more thing. The pressure devices used in these (and many other) studies to measure “strength” are really only measuring tension. That do not measure force production, which would be required to tell if someone was stronger or not. Using this measuring device, someone could read as “super-strong” and really only be “super-tight.”

And one more thing after that. I’ll really try to refrain from pointing out that the C-section group was also the tight/strong pelvic floor group. Chew on that.

The end.

Friedman, Sarah MD; Blomquist, Joan L. MD; Nugent, Joann M. BSN; McDermott, Kelly C. BS; Muñoz, Alvaro PhD; Handa, Victoria L. MD, MHS. Pelvic Muscle Strength After Childbirth. Obstetrics & Gynecology: November 2012 – Volume 120 – Issue 5 – p 1021–1028

Victoria L. Handa, MD, MHSa, Joan L. Blomquist, MDb, Leise R. Knoepp, MD, MPHa, Kay A.
Hoskey, MDc, Kelly C. McDermott, BSd, and Alvaro Muñoz, PhDdt Pelvic Floor Disorders 5-10 Years After Vaginal or Cesarean  Childbirth. Obstet Gynecol. 2011 October ; 118(4): 777–784.

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30 thoughts on “Urogenital Hiatus is not another term for Spring Break

  1. Ha! Good job Katy! I can see all those C section butt tuckers right now. All my prolapse peeps are horrible butt tuckers and have pelvic floors that could crack a nut and sacrums that have never heard the words, “counter nutate.” What they can’t do is sit on a Mikasa ball for 15 seconds without screaming.

    I really appreciate your attention to detail and willingness to tease out the facts. I’m passing this one on. Thanks a bunch,

  2. Love when research gets broken down like this! As a c/s mama (scheduled, no labor), curious if the c/s reference shows whether or not the c/s was planned (scheduled) vs unplanned. And, if planned, was it because of a “failed” previous birth & assumption of being unable to give birth vaginally? In other words, wonder if there’s any way, from this research, to see if there’s a correlation between too tight/”strong” pelvic floor & difficulty giving birth vaginally resulting in a c/s? Will go read it when I’m not at my phone 🙂

    1. Yes! They broke down scheduled vs. non-scheduled c-sections. Lemme go take a look when I have a moment and see whazzup. – KB

    2. Ok, re: c-sections, peak “strength” from greatest to least: No dilation – less than 10cm dilation — full dilation. Average “strength” across the c-section board is equal, but greater than those that delivered vaginally. Thoughts on scheduled/non-dilation c-sections: wondering if these are mal-positioned babies for the most part? Which case, pelvic floor tension also a factor, ya? Verrrrrry interesting.

      1. In my experience as a doula and midwife, the vast majority of cesareans for “Failure to Progress” and “CPD” are actually malposition issues. The relative size of the baby’s head coming through at a posterior or asynclitic angle is much larger than anterior and causes “stalls” at predictable dilations while the baby re-orients. Without patience, providers see this stall as evidence that the baby is too big or the mother’s body does not work correctly and recommend a cesarean. Of course, a certain percentage of pre-labor cesareans are for breech presentation, which is also potentially related to structural issues.

        1. Agree, entirely. I only meant that scheduled sections would likely be related to positional issues. Failure to progress, as you mention, would be the other two groups of sections and are also mal-positional issues! If only every birthing mama and health practitioner had to read through the spinningbabies site as a pre-req. 🙂

  3. I can’t wait for this “science” writers’ take on prostate research. Thank you for penetrating the fog, Katy, and teasing out the useful info.

    Gruvdiva, wouldn’t it be that your prolapsing, butt-tuckers sacra have never heard the word “nutate”? Sorry to be a picker of nits.

    1. Wondering the same thing re: nutation (vs. counter-nutation…) Maybe she means they’ve never heard the term for what they are doing? Maybe?

  4. Katy I am so confused, I love your blog but I am a meathead when it comes to thoroughly understanding biomechanics and physical medicine. Also I’m a naturopathic medical student and I spread the word on your blog any chance I can get with my med student classmates, AND I’m seeing an osteopath for my bladder prolapse who is taking your restorative exercise course (Janet Walker – she got me onto you!)

    So I gave birth vaginally and naturally at home but yet I have this prolapse and I get that it is linked to so many other things and as a med student I sit about 40,000 hours per week which absolutely sucks. But then even if there were no forceps used have my tissues (eg my anterior wall) stretched to the point of no return? Is that the issue? I would love to pick your brain about this whole prolapse thing because honestly even as future doctors we are SO POORLY educated on it – the standard of care even as NDs is similar to MDs and eventually recommend surgery (I KNOW, I KNOW, RIGHT!?)

    Also how are we supposed to interpret that last point: women with C sections have stronger vaginas? That just because your pelvic floor is strong doesn’t mean you can’t also have prolapse? Janet said I likely have a tight and WEAK pelvic floor. ANyways I’m so confused and it’s my second coffee of the day and I really just want to *get* this whole prolapse thing because I want to specialize in treating and preventing it as a doctor.

    Thank you in advance and congratulations on your new bundle of joy!

    – Erica

  5. @Tim, of course they’ve never heard of it, they have no idea that their pelvic bones even move. The whole idea is a giant Ah, ha! I don’t usually use that word with clients. I could have called it tail tucked under and base tipping back, but that’s too many words. Call me lazy.

  6. I’m with you on the annoyance of commentators not including references. It tends to make me a little suspicious that they are missing something else. Maybe I’m just a little paranoid, but thanks so much for putting yours in!

  7. I’ve been struggling with bladder incontinence for years and finally saw an osteopathic doctor who is looking at the incontinence as a possible pelvic problem and has since sent me to holistic physical therapy. Yes, it has opened my eyes to the possibility that child birth and all the other infertility issues and menopause issues that I have struggled with throughout my adult life is part of the problem. Also, needless to say my bladder is sensitive to cola’s and caffeine which exasperates the problem. So, I am on my way to realizing that strengthening those muscles that have weakened over the years is the key to getting healthy again.

    1. I have incontinence as well and with seeing an osteopath and taking out the foods I’m allergic to, it has gone away (and alignment work overall of course). If I eat even a small amount of dairy I just pee at random all day long. Caffeine too for me.

  8. Wow, now I find out that my c-section was my fault, too? This is getting worse all the time.

    Does spinningbabies have anything to say about twins? I was outright told there was nothing to be done, so I didn’t try. Twin A was a footling breach and that was that: c-section mama.

    I’ve managed to live most my life with very few regrets, but they’ve really been piling on lately! 🙂

    1. Cathie, I just had to comment because if your c-section was due to a breech, that is more of a “who your provider is” issue than a pelvic floor issue. Some babies stay breech no matter what. Finding a provider who will help you birth a breech – that is doable! The question is, had you known this information during your pregnancy, would it have changed the outcome? Who knows? Don’t feel regrets. Just move on and do the best you can from now on with your new information.

  9. I have also made a connection with pelvic floor tightness, funky muscular tightness and fetal position. In my own body so I wondered about it in others, Failure to progress, malpositioning, breech, posterior babies, STRONG (aka tight and weak) pelvic floors… I have had this hypothesis for a while!

  10. Katy, I am sure you have heard of the Bradley Method. I taught it for 12 years. I used it during my first few babies’ births. They are loud “do your kegel exercises” proponents. This isn’t to bash them by the way. Just the “kegel” portion of many birthing classes out there. Anyway, they have these exercises that you do contract contract contract (up like an elevator) then release release release like an elevator. You are supposed to do hundreds of these by the end of pregnancy. I was a “pro”. I posted in your squattypotty post about squatting, but I did not add that I believe all those kegels actually led to my baby’s inability to come out smoothly (I pushed for about 4 hours). I had tight muscles to be sure. I think the only reason he came out without a cesarean was that I squatted to birth and I tore.

    I am loving reading your information about pelvic health!!! My kids and I did your foot school, bought your book, are backing it up, etc. etc. Thanks so much!!!

  11. Hi Katy, thanks for doing all that you do. This blog post has been on my mind for several days. I had to C/S and then HBA2C. It went well, but really quick. No tearing, but then at 3 weeks I found prolapse, which was pretty heartbreaking. I wish I would have know about your site before my last pregnancy. I think I have a lot of postural risk factors for PF issues, which I’m trying hard to correct. From the study, it seems my daughter’s big 14+ in. head barreling through can be an issue. I just don’t get the whole tight weak thing. It’s really confusing to me. It seems I may have had tightness issues prior to my VABC, but I wouldn’t have though so. Not a big kegel doer, but don’t have any booty either… So now do I have tightness or weakness or both and how do I find out for myself (or should I just focus on your program and it’ll work itself out)? I’ve seen some OK PTs on the subject, but I think they are confused as me on prolapse. It’s pretty scary to have to find help out there. I can relate to Erica’s post. I’m going into the medical field as well and would love to understand this more as to help spread quality information. I do read just about everything you say on the subject:) I think things are starting to make more sense and have found a nice group of folks over in Pt. Richmond to help. Thanks again and congrats on your baby girl!!

  12. I am 66 and had c.sections three times in my thirties because my hips would hurt so much it felt like they were ripping apart.
    I was told after first one that I was too small in the pelvis. After many years of hip pain and knee pain and sciatica, I finally took control by doing various exercises, using magnetic straps, walking with one leg striding out more than the other….you name it but basically every little bit helped. After Pilates, stretch classes and now getting into Katy’s blogs, I can now almost do a squat which I could not do even when a child and was roundly told off and told I was an idiot if I could not cross my legs or squat like a normal person.
    I can only assume I had a problem from birth or very young but I don’t suppose going for the burn with Jane Fonda helped either as I was a bit of a fanatic for fitness classes then it all went wrong and could hardly move for years. Now hope to actually be able to run for fifty yards before I am seventy. All of the above makes so much sense when seen in retrospect.

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