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The Rhombus of Michaelis

By Cathy Daub with extracts from midwife, Jean Sutton

“The Rhombus of Michaelis?” people ask, “What’s that??”  Most women giving birth have never heard of it before and yet it plays a key part in every birth.  I first heard about it from midwife Jean Sutton in New Zealand.  She went back and studied the old midwifery texts where it was described but now has been largely forgotten in our modern day technological society.

So what is the Rhombus of Michaelis and where is it?  It was identified in the literature as early as 1932 when a New Zealand obstetrician named Corkill discovered an increased space in the outlet of the pelvis during the second stage of labor.  Later, Michel Odent MD identified a possible link to the Rhombus of Michaelis when he described the fetus ejection reflex.  It might also be called the G-spot.

If you take your hand and place it vertically over the low sacrum so your fingers are pointing down towards the gluteal crease, then the flat palm of your hand is right over the Rhombus of Michaelis.  It is in the shape of a kite and includes the three lower lumbar vertebrae, the sacrum and the long ligament that reaches down from the base of the skull to the sacrum.  It is basically a plexus of nerves that serve an important function in labor.

When a pregnant woman is about to give birth, and if her baby is facing towards her spine, the baby’s head will press against the Rhombus of Michaelis nerves causing them to contract and “open her back”  slightly, with the result of hiking her left hip and angling her birth canal towards the back where babies are meant to be born.

Here is a description of the Rhombus of Michaelis as given by Jean:

This wedge-shaped area of bone moves backwards during the second stage of labor 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 Shelia Kitzinger 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.’   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.

Positions that interfere with movement of the sacrum include:

  • Women lying on their backs with knees pulled up which presses their sacrum down, not allowing it to move.
  • Women with an epidural have their nerve supply interfered with so that the impulse for it to happen is obstructed.

Jean goes on to tell us what pregnant women need to know:

  • If they want a short second stage of labor and don’t want to spend a long time pushing, they need to make sure their pelvis will open to make enough space for the baby. This is perfectly safe so long as they have something to hold onto, and that the contraction of the nerve plexus (Rhombus of Michaelis) will relax as soon as their baby is born.
  • They shouldn’t allow anyone else to move their legs while they are in the second stage of labor because they can feel which way to move their body to give birth. Another person moving their legs may lower the leg in such a way that the pelvis goes back into the “wrong place” – and women in labor who are feeling their contractions will know what this means.
  • Movement of the sacrum has the effect of opening the diameters of the pelvis. Being upright the pelvis has more space in which the baby can move and a woman births with the help of gravity instead of against it.
  • Although epidurals are great for pain relief, they 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 (Occiput Posterior) baby needs the Rhombus of Michaelis to move backwards so he has room to turn around so he can come out as an OA (Occiput Anterior)
  • Many women fear damage to their pelvic floor but if they can be in an upright position with their weight forwards so the rhombus is free to move, very little damage is done to their internal anatomy.

Jean summarizes the importance of the Rhombus of Michaelis by saying that:

If midwives want to be assisting women to have as many normal births as possible…to be able to promise women that birth is quite manageable…that they don’t need to have the interventions…that it’s simple and it’s safe, as long as it follows the process, then having the back open is just part of that process.

References:

Sutton J (2000) Birth without active pushing and a physiological second stage of labour.  The Practicing Midwife, Vol 3, No 4. Pp 32-34.

Kitzinger S (1993) Ourselves as Mothers.  Bantam, London.

Corkill TF (1932).  Lectures on Midwifery and Infant Care.  Whitcombe-Toombs, New Zealand.

Oden M (1987) The fetus ejection reflex.  Birth, Vol 14, No 2, pp 104-5.