The Rhombus of Michaelis

Birth-nerd alert! I learned something new! And what I like to do when I learn something new is share it here to let other people know about awesome birthy things.

Today’s awesome birthy thing is ‘The Rhombus of Michaelis’, which plays a big role in physiological birth. Thanks to a post on instagram via North Dallas Doulas, I fell into a little rabbit hole of research.

What’s fascinating though is like there is not a ton of info online about it. Some wicked cool info that I’ll be citing is from a Dr. Sara Wickham who is a midwife, and she in turn is relaying this info from Jean Sutton another midwife, who developed the theory of Optimal Fetal Positioning.

Here is what we do know about the Rhombus of Michaelis:

“The rhombus of Michaelis (sometimes called the quadrilateral of Michaelis) is a kite-shaped area that includes the three lower lumber vertebrae, the sacrum and that long ligament which reaches down from the base of the skull to the sacrum. This wedge-shaped area of bone moves backwards during the second stage of labour and as it moves back it pushes the wings of the ilea out, increasing the diameters of the pelvis. We know it’s happening when the woman’s hands reach upwards (to find something to hold onto, her head goes back and her back arches. It’s what Sheila Kitzinger (1993) was talking about when she recorded Jamaican midwives saying the baby will not be born ‘till the woman opens her back’. I’m sure that is what they mean by the ‘opening of the back’.

Having a birth support rope, shown here from  Birth International,  can help feel more stabilized

Having a birth support rope, shown here from Birth International, can help feel more stabilized

“The reason that the woman’s arms go up is to find something to hold onto as her pelvis is going to become destabilized. This happens as part of physiological second stage; it’s an integral part of an active normal birth. If you’re going to have a normal birth you need to allow the rhombus of Michaelis to move backwards to give the baby the maximum amount of space to turn his shoulders in. Although the rhombus appears high in the pelvis and the lower lumbar spine when it moves backwards, it has the effect of opening the outlet as well.

“When women are leaning forward, upright, or on their hands and knees, you will see a lump appear on their back, at and below waist level. It’s much higher up than you might think; you don’t look for it near her buttocks, you look for it near her waist. You can also feel it on the woman’s back, it’s a curved area of tissue that moves up into your hand, or you may suddenly see the mother grasp both sides of the back of her pelvis as the ilea are pushed out and she is suddenly aware of those muscles that have never been stretched before. Normally, the rhombus is only out for a matter of minutes, it comes out just as second stage starts, and it’s gone back in again by the time that the baby’s feet are born, in fact sometimes more quickly than that.”


How cool is that?! I always knew that our pelvises open to allow the baby to pass through into the birth canal, but I had no idea about all of these details!

There are a few different ways that we prevent the Rhombus from opening up though, such as:

-If women are on their back with their legs up, then their strong gluteal muscles prevent the rhombus from moving backwards

-If a woman has her hands behind her knees and is pulling her legs up towards her tummy, the rhombus is also prevented from moving.

-If she’s got an epidural in, the nerve supply is interfered with so that the impulse for it to happen is obstructed.

“I think we need to get women to understand that, although epidurals are great for pain relief, they actually get in the way of a spontaneous second stage and vaginal birth. In many cases, the reason they’ve got an epidural is that the baby wasn’t in the best position when it started, and the baby in the less suitable positions needs all the space he can get to turn around in. The OP baby needs the rhombus of Michaelis to move backwards so he has room to turn round so he can come out as an OA baby. The woman should then get out without having her pelvic floor damaged.  Pelvic floor damage is a major worry for women, but if they can be in an upright position with their weight well forwards so that the rhombus is free to move, very little damage is done to their internal anatomy.”

Below the butterfly, above the bum, the rhombus of Michaelis. Via  @themidwifemummy

Below the butterfly, above the bum, the rhombus of Michaelis. Via @themidwifemummy

Many anatomy textbooks draw and identify the Rhombus of Michaelis, but fail to assign it a role. “It was identified in the literature as early as 1932, when a New Zealand obstetrician called Corkill (1932) asserted that there is 16cm of space in the outlet of the pelvis during the second stage of labour.”
Nowadays, it seems as though it’s just women’s wisdom. Passed down from midwives as another external sign of how physiological birth is progressing. I truly believe now that understanding this area increases chances of having a normal physiological birth; meaning how our bodies know how to give birth instinctually, if no troubles are to occur.

Did you know about the Rhombus of Michaelis? Isn’t it fascinating? The human body continues to astound me!