In one of my first lectures on anatomy and physiology, I dropped the doll and pelvis set we were handing round.
As we were in a seminar room with a pitched floor, the doll bounced down the steps for quite a long way with a clonk-clonk-clonk noise before another student caught it. Not a great omen.
I also struggled quite a bit with the birth mechanism side of things as I’m not a very visual person. Cycling has been my main form of transport for about ten years and my partner still laughs at me trying to lock my bike to stuff because I can never get the shapes to line up.
But even with my dire relationship with spatial awareness, I still managed to learn everything I needed to as a student midwife.
In this post I wanted to go through the most typical mechanism of birth as maybe like me you struggle a bit and maybe also like me you find it utterly fascinating.
Having a good knowledge of the mechanism of birth will help you as a midwife visualising what’s going on when a woman’s in labour and helping her optimise positions.
It’s essential knowledge if you want to be a successful midwife promoting physiological birth.
There are many ways for babies to be born, they do all kinds of interesting things in the diameters they have available as they journey through the pevis and birth canal, but knowing this route that's most typical is a great base for learning all the others.
First watch this great summary video which simply explains the passage of the baby through the pelvis:
Now we can fill in a few more details.
The Mechanism Of Typical Birth:
Descent: The baby’s head enters the pelvis in a traverse position. This means the baby’s face is either facing towards the left or right of Mum. As the video above says, this is because the widest part of the baby’s skull is fitting into the widest diameter of the pelvic outlet.
Flexion: As descent happens, we hope the baby will tuck his or her chin in, touching the chest, as this makes for the very smallest diameter of the baby’s head coming through the pelvis.
Internal Rotation of the Head: With contractions and pushing, the baby’s head reaches the pelvic floor. The pelvic floor is a sort of cradle of muscles, ligaments and fascia which is between the pelvic cavity and the perineal area below.
When the baby’s head gets to the pelvic floor, it will turn. Because the smallest bit is the vertex shown in the image below, this is what will fit into place and emerge from Mum first.
Crowning: For a little while there is usually some ‘two steps forward, one step back’ type pushing where the presenting part progresses and recedes. Eventually, the occiput will come under the pubic arch and the head will crown and not recede anymore.
Extension: The fetal forehead, face and chin ‘sweep’ the perineum.
Restitution: Now the baby’s head is born it will turn either towards Mum’s left or right thigh, depending on the position of the shoulders (the baby’s head will right itself with the shoulders).
External Rotation: Now the shoulders will rotate internally – the largest diameter of the pelvic outlet is from top to bottom in the image below, or otherwise known as the ‘anterior-posterior ‘(AP) diameter. This is where the baby will position their shoulders.
Lateral Flexion: The head will restitute back into alignment with the shoulders. The uppermost shoulder is delivered (known as the anterior shoulder) under the pubic arch, followed by the posterior shoulder and the baby is fully born!
Of course, you’ll need to be able to describe all the different diameters of the fetal skull and pelvis, the names of bones, sutures and fontanelles, and other details for exams as a student midwife.
But if you know the physiology inside and out (haha) you don’t actually need to know the names of all the different bones and diameters to practice well.
Though it does help when communicating with medical staff and it can be fun to have that lingo at your fingertips!
Do remember Mums probably aren’t going to know technical anatomy and physiology details so it’s always good to be able explain things in clear terms, without the jargon.
Ina May Gaskin in Spiritual Midwifery is particularly skilled in explaining things in a down to earth way.
Drawing lots of diagrams, using revision cards and practising with a doll and pelvis over and over will make things much easier to learn.
In fact, there's good evidence that combining creativity with learning makes you remember things more effectively.
So my questions for you today are…
1. Was this post helpful in understanding the basic mechanism of birth?
2. What’s a creative way of committing this to memory, what's one thing that could make all the difference to your learning?
3. If you’re a lecturer or mentor, how do you help your students learn the mechanism of birth?
Leave me a comment letting me know.
I hope you’re having a great week and not melting! Thanks for spending your valuable time reading about birth and it's an honour you're here on Midwife Diaries.
Ellie xx
Hi!
Thank you for this brilliant resource. I feel it has given me some great headstart insight into the mechanism of birth – by using visual of the video and with the help of description and seeing what happens in slow motion really helped me!
Keep up the good work 🙂
Claire
Hi Elly,
Thanks I found this post really helpful! Next semester I’ll be studying anatomy and physiology, so it was great to read about the positions and process.
Thank you so much for writing, your insights are always inspiring and helpful!
Emily
Thanks Emily, good luck and have fun with your next module!
Dear Thanks ,your some describe birth mechanism ,your lecture help me , God bless you .
Sadly I see your animation involves a recumbent, immobile womans pelvic girdle plus a passive baby passager ! As few women in out of hospital birth assume this position or role I suggest this is not Physiological labour or birth! I prefer the short birth here https://www.ted.com/talks/alexander_tsiaras_conception_to_birth_visualized which shows an active baby! The “mechanisms” information as you indicate is useful for managed deliveries involving doctors or if baby becomes stuck. 40 years of midwifery especially the last few doing mostly homebirth in New Zealand has taught me that what is essential for Physiological labour and birth is a knowledge of Hormonal Physiology and what can positively and negatively impact on it as explained by Dr Sarah Buckley here; http://www.nationalpartnership.org/research-library/maternal-health/hormonal-physiology-of-childbearing.pdf
I’m not a midwife, or studying midwifery but as a childbirth educator this post was so incredibly helpful! I loved the video and this will be great to show in my childbirth classes. I have crap spatial ability too, so I really related to your story and I get a cold sweat before demonstrating the baby’s descent and rotation through the pelvis, especially because my doll and pelvis set are not the best fit and it’s hard to demonstrate a smooth descent (and not an agonising posterior labour to nervous parents-to-be!) Thank you – I love reading your posts.
Thanks Tanya, glad it helped! It is not the most simple thing to describe sometimes. Good luck with your classes, sounds like you’re doing good things in the world x
This is fab Ellie. I like the Dutch pelvis model. It doesn’t simulate flexion, but really helps to visualise the changing diameters and the pelvic floor!
Sarah (3rd year stmw)
Hi Ellie,
I am a hypnobirthing teacher and wannabe midwife (when my kids are older, I hope I’ll get the chance to train).
Thanks for sharing this, it’s something that’s been explained to me a few times but I find the visual is always over before it started so the break down you have written combined with me stopping and staring the video is really helpful. I may even be able to talk to parents about this part now! Thank you!
Danielle x
P.s
Loved your book New Walk, excited for the next one!
Hi Ellie, this is a Fab post, thank you!
Would you be able to repost the video showing the mechanisms of labour please it isn’t working.
Thank you again!
Sam