Pelvic Inlet vs Pelvic Outlet: How your baby navigates your pelvis

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Your Pelvis Isn’t Fixed – It Moves!

A lot of people imagine the pelvis as a rigid, bone ring. But in reality, it’s a dynamic, flexible structure. The bones, ligaments, and joints of your pelvis move and shift throughout pregnancy and labour. When we talk about biomechanics in birth, we’re talking about how to use those movements to create more space for your baby to rotate, descend, and be born.

There are two key spaces in the pelvis that matter in labour:

The pelvic inlet (where baby enters the pelvis)
The pelvic outlet (where baby is born)

And each of these spaces opens with different types of movement.

What Is the Pelvic Inlet?

The pelvic inlet is the upper opening of the pelvis – the space baby first needs to navigate when labour starts.

To open the pelvic inlet:

Tilt the top of the pelvis forward
Encourage space at the back of the pelvis (the sacrum area)
Widen the space between your iliac crests (the top bones of your hips)

Best positions to open the inlet:

Standing with a forward lean (e.g. leaning over a surface or birth ball)
Hands and knees with the bum slightly up (not arched too low)
Forward-leaning inversion
Lunges or asymmetrical movements
Side-lying release to release tight ligaments that may reduce inlet space
Your pelvis opens an extra 28% in upright and forward positions

These positions are helpful in early or latent labour, especially if baby is still high or not yet engaged in the pelvis.

What Is the Pelvic Outlet?

The pelvic outlet is the lower opening of the pelvis. This is where baby is born. In the final stages of labour, baby needs space at the front of the pelvis and the ischial tuberosities (the “sit bones”) need to widen.

To open the pelvic outlet:

Tilt the top of the pelvis backward
Encourage space at the front of the pelvis
Allow the sacrum and coccyx to move back freely

Best positions to open the outlet:

Squatting (with support or using a rebozo or partner)
Kneeling upright or all fours with knees close and bum low
Side-lying with the top leg forward
Using a birth stool or supported seated squats
KICO – Knees In Calves Out

These positions are ideal for the second stage of labour – especially when baby is low in the pelvis and ready to be born. It is normal to see women instinctively close their legs here, this in fact allows more space in the pelvic outlet.

The Pelvic Cavity and Baby’s Rotation

Between the inlet and outlet is the pelvic cavity – the middle part of the pelvis. This is where baby often meets the pelvic floor, a supportive sling of muscles that provides feedback and gentle resistance. As baby presses against these muscles, the pressure helps encourage them to rotate into a more optimal position – usually turning from occiput transverse to occiput anterior as they descend.

This process of rotation is a key part of labour. When the pelvic floor is balanced and the body is in a position that gives baby space to move, they’re far more likely to rotate successfully and continue descending without delay or intervention.

Trusting Your Body’s Urge to Move

Here’s the amazing thing: your body often knows exactly what to do. Many women naturally move into positions that support their baby’s rotation – simply by responding to what feels good and what doesn’t. If your baby is trying to turn but struggling, you might feel backache, pressure, or just an inner urge to sway, lean forward, change sides, or rock on all fours. That instinctive movement isn’t random – it’s helping your baby too. I’ve seen women stretch their legs up walls, push their legs out in all sorts of weird and wonderful positions to help their baby be born.

However, lying on a bed restricts this natural feedback loop. It limits movement and reduces space, especially in the sacral area. If you have an epidural, you may also be less able to feel those subtle cues from your body. While epidurals are a fantastic option for many and can be incredibly helpful in labour, they can make it harder to notice when baby needs help moving. This is why intentional positioning becomes even more important – with support from your birth partner or midwife to shift your body in ways that still promote pelvic space and baby’s descent.

Why This Matters

If you’re in a position that closes the part of the pelvis your baby is trying to move through, it can slow things down – even if you’re having contractions! This is why some labours stall at 4–6cm or take longer than expected when baby is trying to engage or rotate.

By understanding the difference between the inlet and outlet, you can:

Choose the right position for the right stage of labour
Help baby engage if they’re high or floating
Support rotation if baby is back-to-back
Avoid unnecessary interventions by keeping labour moving naturally

Want Help Knowing Which Position to Use When?

Inside The Birth Chapter, you’ll get:

A complete guide to pelvic biomechanics
Step-by-step instructions for positions that open the inlet and outlet
A printable cheatsheet for birth partners and midwives
Plus, full hypnobirthing and antenatal education videos, so you’re not only physically prepared, but mentally and emotionally supported too

This is the kind of knowledge that makes you feel confident and calm – because you understand what’s happening in your body and how to work with it.

Pelvic Inlet vs Pelvic Outlet: How your baby navigates your pelvis

Your Pelvis Isn’t Fixed – It Moves!