Your pelvis is your baby’s portal to the world and is a truly amazing one at that. With its sling of pelvic floor muscles that lay in its base, it provides the nest to support your baby as he grows. As your baby grows and comes nearer to term, you begin to produce a hormone called Relaxin which really allows the pelvis to show off its talents.
The pelvis is basically made up of 3 parts – the ilium, the sacrum and the coccyx. These are all joined by ligaments that respond to the hormone Relaxin by softening and allowing your pelvis to actually move and enlarge to accommodate your baby’s smooth journey down the birth canal.
The Symphytum Pubis (the ligament between your pubic bone) can expand up to ½ an inch to make room for the baby’s head. The 2 sacro-iliac (hip) joints at the back expand from side to side and also move in a pivot action to increase the area for your baby to pass through. The sacro-coccygeal joint also loosens so that the coccyx moves out of the way as your baby is born.
Now as astounding and ingenious as this ability to ‘billow’ open is, it is actually dependent on the position you might take to give birth. For example, the stereotypical scenario of lying on your back or reclining actually decreases the amount of space that your baby has to have a great journey by as much as 30%! Whereas upright positions that also work with gravity really allow the pelvis to show off its full potential because the sacrum and coccyx lift up to open and expand the outlet and give your babe the room it needs. (These would otherwise be restricted by lying down) More often than not a woman will instinctively want to squat, kneel on all fours, or be in an upright position to birth. We already know how to do this! But it doesn’t stop there, the bones in your baby’s skull have been deliberately left un-fused (you may have heard of the fontanel) this allows your baby’s head to mould to the shape of the birth canal in order to ensure a smooth transit.
And yes, after the birth everything returns to normal!
It is worth noting that it is a myth that woman’s pelvis are too small, etc, particularly if a big baby is expected. Women who are petite have successfully given birth to babies 10 pounds and larger. The only true CPD (Cephalo-pelvic disproportion – baby too big in relation to pelvic outlet) is in the case of pelvic deformity from conditions such as rickets, malnutrition as a child or from previous injury. Having said that, the interplay of hormones as well as the pelvis’ mobility and trust, has meant that some women who’ve experienced a broken sacrum or coccyx have gone on to birth vaginally. This includes myself.
If a large baby is expected, there is a wonderful technique that the partner can help mum with during the pushing phase (if it looks like more effort is required, again take cues from mum). With the support person standing or kneeling behind her, pressing both iliac crests (top of hip bones) toward each other during a pushing rush will help open the pelvic outlet that little bit more.
Of course, it must be noted that if a woman desires to birth on her back, her side, her knees, squatting, sitting, in water, on a bed, beanbag, chair, hanging onto the kitchen sink or pulling on a rope, or in her car on the side of a freeway then if that is where she is most comfortable then that is where she will birth because her body will be relaxed enough to make it happen.