Episode 124 The Pelvis

Are there four types of pelvis, that's what we are taught but is it true? Are we sometimes misinforming women about their pelvic shape and ability to give birth?

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Thank you all for listening, My name is Florence Wilcock I am an NHS doctor working as an obstetrician, specialising in the care of both mother and baby during pregnancy and birth. If you have enjoyed my podcast please do continue to subscribe, rate, review and recommend my podcast on your podcast provider.
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Florence Wilcock: [00:00:00] Hello, my name's Florence. Welcome to the obs Pod. I'm an NHS obstetrician hoping to share some thoughts and experiences about my working life. Perhaps you enjoy, call the midwife, maybe birth fascinates you, or you'll simply curious about what exactly an obstetrician is. You might be pregnant and preparing for birth.

Perhaps you work in maternity and want to know what makes your obstetric colleagues tick or you want some fresh ideas and inspiration, whichever of these is the case. And for that matter, anyone else that's interested? TheObsPod is for you,

episode 124. The pelvis. I've been thinking a bit about this episode for some time. [00:01:00] Pelvic shapes, the bony pelvis, the bowl like structure that the baby has to pass through on its journey down the birth canal. I've been turning this topic over in my mind for a couple of reasons. The first reason, Was when I was reading the Black Maternity Experience Report because there were comments in there about in inverted commas, the African pelvis, and I'm sorry to say that that rang a bell at some point during my training, either as a medical student, Or a junior doctor.

I definitely remember being taught about the African pelvis, so that prompted me to think really, is that really what we [00:02:00] were taught? Perhaps I should go back to my textbooks and have a look. The other reason I've been thinking about the pelvis is because of the increasing use of biomechanics. And this is the idea that the pelvis isn't a rigid skeletal bony structure after all, but actually is a mobile structure with multiple joints and how one moves in labor might influence the size and shape of that bony skeletal structure.

And I listened to a wonderful episode of the Birth Ed podcast with Molly, the midwife, who does a lot of training on biomechanics. So for these two reasons, I wanted to think a little bit about the pelvis, partly because when topics like these crop up, I [00:03:00] like to review what I know or what I think I know, and then find.

What's new? So here goes the pelvis. Regular listeners will know I have a textbook, a 1933 Glasgow Manual of Obstetrics. So I thought in thinking about the pelvis, I would go back and start with that. And in my episode where I talked about a hundred years of progress, many of you will remember that I talked then about the very distorted pelvic shape.

Contained within that book as such large numbers of women at that point in time had rickets and therefore significant pelvic deformity, which impacted hugely on their ability to give birth to their babies. So whilst in my medical student mind, I'm thinking about having been taught about different types of [00:04:00] shapes of pelvises when I go back.

In time to the Glasgow Manual of Obstetrics textbook from the thirties. Those pelvic types do not exist. There are lots of diagrams. It is true of different pelvic deformities and contractions, but they're all pathological. They're not in inverted commas normal shapes. They're what may happen to the pelvis with disease.

But there are clear descriptions of how to try and measure the pelvis, both with vaginal and external examination, and there's certainly no mention of that inverted commas African pelvis comment in that book. So next I thought I would [00:05:00] turn to my. Anatomy textbook. This is the book that I used as a medical student, clinical Anatomy for medical students by Richard Snell.

It was the absolute anatomical Bible. When I trained and qualified turning the pages of my copy, I discover that my edition dates back to 1986. Not surprising, really given I was starting out as a medical student in 1987, so if I turn to the page on the pelvis, there they are those four different types and shapes of pelvis that I remember being taught and they taught about the difference in the female pelvis.[00:06:00]

Versus the male pelvis. They talk about the pelvis being shallower and the bones smoother in the female pelvis than male. The size of the pelvic inlet being very similar between the two sexes, but in female, the pelvic cavity being larger and cylindrical, and the pelvic outlet. In both the anterior, posterior, and transverse diameters, so that means front to back and side to side.

Then it defines the four types of pelvis. And it's interesting because I've just told you that looking back in my textbook from 1933, these types of pelvis don't exist and here is the reason. [00:07:00] This classification of Pelvises was designed by Caldwell and Malloy in 1933. They divided the pelvis into four discreet groups, Gynaecoid Android, anthropoid and Platypelloid

The Gynaecoid pelvis they said is present in 41% of women and it's the typical female pelvis, the Android type present in around 33% of white females and 16% of black females is the male or funnel shaped pelvis with a contracted outlet. Let me pause there. Is that where. In inverted commas theafrican pelvis is coming [00:08:00] from the anthropoid type pelvis present in 24% of white females and 41% of black females is a long narrow and oval shape pelvis.

And then we have the Platypelloid type present in only around 2% of. , and this doesn't distinguish between Caucasian or Afro-Caribbean and is a wide pelvis flattened at the brim with the sacral promontory. That's the bit at the back pushed forwards.

So I distinctly remember having to learn these four types of pelvis.

To be honest, I found it quite confusing. It's not easy to remember obscure classically [00:09:00] derived names for different shapes and sizes, and it seemed quite irrelevant at that point in my career. Why would I need to know? There are four types of pelvis in the book. There's then a description of how to make internal pelvic assessments by vaginal examination.

And this interests me because in all the time I've practiced obstetrics and gynecology, we've never actually discussed how we might assess a pelvis through vaginal examination yet. This is something clearly. That doctors at some point in time were routinely undertaking, and I do remember a point when I was a medical student where part of your antenatal check was an initial vaginal examination, and maybe [00:10:00] this is what one was supposed to be assessing, but this certainly isn't part of our routine check anymore.

Thank. So there's a very clear description of how to assess the different diameters of the pelvis. First of all, the pubic arch spread the fingers under the pubic arch examine its shape. Is it broad or angular? You should be able to rest the examiner's four fingers comfortably in the angle below the synthesis comfortably.

Hm. Not that comfortable for the women. I wouldn't imagine. Lateral walls palpate the lateral walls that mean feel and determine whether they are concave straight or converging. The prominence of the ischial spines, those are the little bony prominences you can feel either side and the position of the [00:11:00] sacrospinus ligaments are noted posterior.

Palpate the sacrum to determine whether it's straight or well curved. Finally, if the patient has relaxed the perineum sufficiently, this poor woman, I doubt, she's very relaxed by now. An attempt is made to palpate the promontory of the sacrum, second finger of the examining hand placed on the promontory and the index finger of the free.

Outside the vagina placed at the point on the examining hand where it makes contact with the lower border of the synthesis. Trying to imagine even trying to do that. Ah, there's a helpful diagram. The fingers are then withdrawn and the distance measured. This gives the measurement of the diagonal conjugate, which is normally about five inches or 13 centimetres.

[00:12:00] Then estimate the anterior posterior diameter from Sacco coccygeal joint to the lower border of the synthesis. Maybe it doesn't matter. I was never taught this. Maybe this is a heap of old rubbish ischial tuberosities. The distance between the ischial tuberosities, those are on the outside can be estimated by using the closed fist.

Measuring about 10 centimeters, but difficult to measure exactly. No kidding. You mean all the other measurements were accurate then There is a little caveat. Needless to say, considerable clinical experience is required to be able to assess the shape and size of the pelvis by vaginal examination

marvelous. Just thinking of all the poor women that would need that examination for me to be able to be experienced to. . So when I do a vaginal examination, now, [00:13:00] I must admit, the thing I tend to notice, apart from obviously the position of the head and things I've discussed earlier on about the progress in labor is more the pubic arch.

How narrow or wide is the pubic arch? How prominent is the sacral pulmontory? Those tend to be the two things that I. And yes, I can think about is there space, um, and whether I can fit my hand in the vagina. And although that sounds awful actually, if you think about the size of your hand in comparison to a baby's head, that's not a bad guide that the baby's head will be able to come through.

If I can get my hand in, if I can't get my hand in, then actually it could be that there's not a lot of space between the sac called promontory and the pubic arch. So that's 1986, right? Let's move forward. In my career, it's 1997. [00:14:00] I've just become a registrar and I distinctly remember having to do some kind of a presentation or a little project.

Breech presentation, breech birth, and the use of pelvimetry , would pelvimetry that is x-rays of the pelvis and measurements of the pelvis be useful in predicting which women would be able to have a breach birth safely. I've trawled through the many things on my shelf because I'm a bit of a. And I expected to be able to just pick it up just like that, but for once in my life, it seems I've got rid of it or I can't lay my hands on it.

So I turned to the RCOG G library [00:15:00] and sure enough, 1997 find a paper all about the use of pelvimetry in breech presentation. And traditionally pelvimetry was x-ray. But of course, in the modern era, we have other options because the pelvis isn't just bony skeletal, there are muscles involved. So the paper that I remember is actually about could we use MRI or magnetic resonance pelvimetry.

For women with a breach presentation at term, it talks about the fact pelvic imagery is widely used, but that its clinical value hasn't been established. And rather than doing x-rays, they use MRI and [00:16:00] essentially they concluded that it wasn't terribly helpful. It might help you do what's. Selective breech birth.

So where you select which women you think might be more able to have a vaginal breech birth than other women. But there actually weren't any differences in the women that had pelvimetry versus women that didn't. When you look at the cesarean section rate, so breach is a whole nother topic and. I've got a whole episode bottom down about breech babies, but the principle of measuring a pelvis, whether that is with x-ray your hand, as I've just described in the 1986 book, or with the more advanced magnetic resonance imaging mri, [00:17:00] not particularly.

And I've explained this to women in clinic, perhaps they're coming, considering whether a vaginal birth after cesarean is a sensible thing for them to approach. Maybe they were told last time their baby was too big for their pelvis, or they were told that there was a problem with their pelvis because we can make off the cuff flippant remarks about things like that.

Without really thinking what the ramifications and implications are. In fact, only recently I've had a woman who was told after her first birth that absolutely she couldn't have a vaginal birth, that there was a problem with her pelvis and being sensible. She decided to question this and get a second opinion and challenge this.[00:18:00]

I quite appropriately did say because it wasn't true at all. So we need to be very careful about the comments we make about women's pelvis. But when women ask me, can you measure my pelvis? And I tell them that actually the evidence is, it doesn't make a difference. It's not helpful. It doesn't give us useful information.

They accept that. But I've always found that a little bit strange. Why can't we measure it? Why wouldn't it be useful? Why is the evidence so poor? So enter biomechanics, this isn't something that I'd heard of until recently. I know, sounds really dim, doesn't it? But the. Of the pelvis actually [00:19:00] being mobile and flexible and the dimensions changing not only with the changes of pregnancy, but the changes in positions Women adopt and you see them instinctively adopt.

When birth is undisturbed and unmedicated, then it starts to make sense. Because the actual measurements we take aren't dealing with the fact that the pelvis is actually dynamic. If you want to understand more about this, I am absolutely not the expert and I highly recommend you have a little look. Or listen to the birth ed podcast with Molly, the midwife who runs a lot of courses on biomechanics for midwives and women alike.

But we are [00:20:00] increasingly using biomechanics on the labor ward to try and help babies turn into good positions, preventing what we call mal position, where the baby's in an awkward position and that's slowing the labor. And to aid and assist descent of the baby's head. And we can use these dynamic movements even if a woman has an epidural and is relatively immobile.

So when I start to think about the pelvis as a dynamic object, then it starts to make complete sense Why taking measurements of that object at a single point in time in one position, Is useless, totally pointless and not going to give me good information. So thinking a little bit more about this episode, [00:21:00] I thought I will look at the Cochrane database.

Is there anything new I should be considering in the modern era? Is pelvimetry not helpful in deciding mode of delivery. And the Cochran database has published a useful little summary back in 2017, and it talks about all different forms of pelvimetry X-ray, CT scan, or mri. And what it found was just as I said, that the evidence is poor quality.

There's very little evidence and it doesn't seem useful to measure the size of a woman's pelvis in helping predict which women will or won't be able to have vaginal birth. And I suspect that comes [00:22:00] back much more. As I said to the idea of the pelvis being dynamic, and I've learnt this in my own personal.

Having had back problems for some years, I started first Pilates and then yoga, and oh my goodness, I discovered my pelvis moves. I can do a pelvic tilt, I can do a pelvic clock, I can move my pelvis around, and actually that has a massive impact on my posture. Pain in my back, which is a complete thing of the past.

Now I've learned how to keep my back and my pelvis flexible fluid dynamic. Okay, let's go back to the beginning. What about those four [00:23:00] classifications of the pelvis? Do they exist?

I love a little bit of research, a little bit of reading to help me think about a topic when I'm preparing the podcast, and I found a great little article in the British Journal of Midwifery, these guys, and I've put a link in the program notes. They decided to reevaluate that Caldwell Malloy 1933 classification of female pelvic.

Traditionally and still currently taught to students of midwifery and medicine. And they did this by using modern pelvimetric methodology and geometric morphometric analysis techniques. And what they found is, guess what? That it's. [00:24:00] Doesn't seem to be correct. There does not seem to be obvious clustering into the four distinct types of pelvis, gynaecoid, anthropoid, Android, and Platypelloid, and actually there's a much more amorphous, cloudy continuum of shape variation Who'd have thought?

So the idea of this basic pelvic classification, which I have always found impossible to remember, I'd always found difficult to explain or think about with students. Actually we've spent 60 years of teaching something potentially that totally isn't. And this article also tackles that [00:25:00] in inverted commas, African pelvis, the potential racist criticisms of the classification.

This study is completely fascinating and suggests that a lot more study needs to be done and that the way we are teaching traditionally midwifery, Medical and related professionals that there are four distinct types of female pelvis really need reviewing and reevaluating. It talks about it being much more helpful to have an awareness that pelvic shape has many components that may affect childbirth, and that to explain difficulties in labor obstruction.

Or a high head, the baby's head not descending into the pelvis. To attempt to [00:26:00] explain these events by categorizing the pelvis is not necessary, not affect the management of labor. And I would add, or possibly inaccurate and unhelpful. And I definitely remember at some point as a junior, Having it explained to me that African women were less likely to have a baby with an engaged head before labor, that the baby's head was typically higher up and then when contractions started, would engage and come down through the pelvis at a later point.

In comparison to Caucasian women, I have no idea. Why I was told this, or on what basis I was told this, but we have a problem if [00:27:00] this is the way we are educating people. Because if I hadn't read the comment about an African pelvis in inverted commas in the black maternity experience, I would not be thinking and questioning what I was taught and the fact that actually this is a microaggression and inbuilt racism.

Right? That's a little tour of my thoughts on the pelvis. What about my zesty bit? Well, if you are a professional and you're like me and you struggle to think about all the different types of pelvis, don't worry because you can pretty much bin them. But I would like you to come away and reevaluate what you think you [00:28:00] know about the pelvis and remember that it's dynamic and have a look at biomechanics and.

How you can help women understand the mobility of their pelvis and that pelvic shape will change depending on what they do, what positions they adopt, and the hormonal changes of pregnancy and birth. If you are pregnant listening to this and people tell you things about your pelvis or have told you in the past, so.

About the shape of your pelvis or the way your pelvis and your baby fitted or didn't fit in a previous birth. Then question that. On what basis were they making these comments? Perhaps go back to your maternity notes and discuss it with a health professional if you're planning more babies, [00:29:00] because clinging to those misconceptions may end up giving.

Poor advice on which to take decisions about your future pregnancies or births. Know that your pelvis is not a rigid skeletal structure, and there is a lot that you can do to keep pelvis mobile. And adjust the different diameters both during pregnancy to keep you comfortable and with your pelvis well aligned with your changing body shape, but also during labor to help the journey of your baby through the pelvis and down the birth canal.

I very much hope you found this episode of the OBS Pod. Interesting. If you have, it'd be fantastic. If you could subscribe, rate, [00:30:00] and review on whatever platform you find your podcasts, as well as recommending the obs pod to anyone you think might find it interesting. There's also tons of episodes to explore in my back catalog from clinical topics, my career and journey as an obstetrician and life in the nhs.

More generally, I'd like to assure women I care. That I take confidentiality very seriously and take great care, not to use any patient identifiable information unless I have expressly asked the permission of the person involved on that rare occasion when it's been absolutely necessary. If you found this episode interesting and want to explore the subject a little more deeply, Don't forget to take a look at the program notes where I've attached [00:31:00] some links.

If you want to get in touch to suggest topics for future episodes, you can find me at the obs pod on Twitter and Instagram and you can email me the ops pod gmail.com. Thank you for listening.

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Episode 124 The Pelvis

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