Key through the keyhole- the Cardinal movements of labor

When we unlock the front door to our homes the key we insert into the lock fits in one specific way, and it must turn at the right time in order to release the tumblers within the lock mechanism and open the door. Similarly, while it might seem like a baby simply slides through its mother’s pelvis to be born; in fact the baby makes a series of twists and turns in order to emerge. Called the Cardinal movements, these extensions and rotations help the baby find the best fit to spiral down and out of the body. Far from being a straight channel, the pelvic birth path is in fact curved from the top to the base, as well as different widths depending on which level of the pelvis the baby is moving through. Understanding how baby moves within and is guided by the structures of the pelvis can be immensely helpful in learning to work with your own individual labor.

The cardinal movements are in order:

• Engagement

• Descent/Flexion

• Rotation (sometimes called internal rotation)

• Extension

• Restitution (or external rotation)

• Expulsion

Engagement

The first thing that must happen for the baby to navigate the birth path is they have to get into it. This begins with the baby’s head moving into the upper oval of the lower pelvic bowl. For some births this may occur before labor has begun, and for some it will not occur until much later. The head will often initially engage looking to the right (ideal) or left of the pelvis. This is because the inlet of the pelvic bowl (the circle formed by the pubic bone, illium, and sacral promontory, is wider from side to side than front to back, and the baby’s skull is wider front to back that side to side. So the direction with the most space has the baby looking to the side, hopefully with the spine slightly towards the front side of the body because of what happens later in the cardinal movements.

Descent/Flexion

Once the head is through the inlet of the pelvis the baby is moved further down against the opening cervix by the contractions of the uterine muscle fibers. This downward pressure helps to flex the baby’s neck more fully, bringing the chin into solid contact with the chest. This is a key step because a head with the chin tucked into the chest literally presents a smaller circle to the pelvic bones around it, where a head that is extended- that is with the chin lifted away from the chest- will seem to be larger even though the baby is in fact the same size. In my experience as a doula, it is far less about the baby’s size and much more about how flexed in the chin combined with the next cardinal movement that can impact the course of labor. Even a “very large” baby, will usually be able to navigate its mother’s pelvis, if its head flexes into its chest.

Rotation (Internal rotation)

I think this is the one we are simultaneously the most and the least aware of when it comes to labor. As the head descends and begins to open the cervix, the baby moves into the middle area of the pelvis, which is governed by the pelvic floor. Where the top of the pelvic bowl was wide side to side, the pelvic floor muscles of the levator ani are open front to back in the pelvis. This means that the baby’s head needs to rotate so the long axis of the head can line up with the opening of the pelvic floor. Here’s the turn of the key in the keyhole, and the direction things spin has an immense impact on the course of labor. Ideally baby rotates in what is sometimes called the “short arc” meaning they turn 90 degrees so their spine moves to the front of their mother’s body, and their nose looks towards her sacrum. This is the ideal position, and often makes for a faster labor. The other option, sometimes called the “long arc” is when instead of turning just 90 degrees, baby tries to go the other way and effectively has to rotate 270 degrees to wind up in the same bum facing position. The downside is that while making this longer turn, the spine has to turn into mom’s spine, which makes it harder to keep the chin tucked into the chest- cue back pain from internal pressure on pelvic bones! Commonly referred to as “back labor” this can actually manifest as pain anywhere within the pelvis, and even along the pubic bone in the front, since the head is now pressing bone into bone from the inside. (Think that’s no big deal? Try pressing hard on your shin to get an idea of the difference between bony pressure, and strong muscle action.) Long arc rotations often wind up with longer labors and slower cervical dilations because the head doesn’t press as fully into the cervix while it is rotating to align with the pelvic floor. Once it has aligned, then the head can descend further, and the cervix can open. As a doula I have seen numerous labors where the cervix dilated very quickly to one number, and then paused as the baby spun in the middle pelvis to align with the pelvic floor. With patience and often a lot of labor support, dilation was able to resume once the pieces had lined up again. The head descends through the upper pelvic floor layers, and labor continues.

Extension

Once the head is through the pelvic floor we come to the cardinal movement that I find the most amazing and cool. Extension. Having dropped well into the lower pelvis, facing their mom’s back, the back of the baby’s head now comes into contact with the underside of the pubic arch. But instead of this being bone on bone pressure like during an OP presentation, this pressure begins to trigger a reflex in the baby’s nervous system that cues them to try and lift their chin off their chest. Think for yourself of anytime someone has pressed on the back of your skull- especially by surprise. Our body’s have a built in reflex which leads us to lift our head in an effort to perhaps see what might be pushing on our head from the back. Same thing for the baby! And as the head extends the neck, this action literally draws the baby underneath the pubic arch moving them down further in the pelvis. It should be noted that this is also when mom usually feels a strong urge to bear down and push if there is no epidural. Initially this lifting of the chin creates a rocking motion, where the head moves down with the contraction, but the retreats in between. This is due to the skull plates slowly molding to narrow the diameter of the skull (totally safe for baby), as well as mom’s pelvic bones widening (also totally safe more mom). When the two circle of the head and the pelvis align to the same diameters, the baby can finally lift their chin fully and pull their head under the pubic bone and fully into and through the pelvic floor in what is usually called crowning and birth. When demonstrating this with models I always imagine this is the final moment of “What?” from the baby as they investigate who has been bumping the back of their skull.

Restitution (External rotation)

Once the head is birthed, there is one final movement the baby must do before they can fully fit through the keyhole of the pelvis. The head has spun to align with the pelvic floor, but the shoulders are still aligned with the top inlet of the pelvis. This means baby’s body must make one final 90 degree rotation either right or left to align the shoulders with the mid pelvis and pelvic floor. This usually happens fairly seamlessly, since an infant’s head is actually the largest portion of their body, and once that is birthed, the top and the bottom shoulders follow suit fairly easily. Providers will often quietly watch to see which way the head begins to spin following crowning, which then lets them guide the body out as they receive the baby. With possibly one or two pushes, the body usually slides out all in one movement, and the baby is placed directly on its mother’s body as the bonding process begins. Happy Birthday, Mom and Baby!

Following the birth, other muscles within the uterus contract to tourniquet the blood vessels to the placenta. The placenta detaches and drops to the lower uterine segment, and since the placenta has no bones, it usually slides out with possibly only a gentle push from mom.

Far from being a straight canal, the birth path through the pelvis is a curved and spiraling dance between mother and baby. Movements like hip circles, pelvic tilts, side lunging, and forward tilted squatting can assist in making space in certain areas of the pelvis which in turn can help the baby move through and out into the world.

Helpful movements during labor

• For the Inlet (upper pelvis)

  • Hip circles- especially sitting on a yoga ball

  • Tucking the tail bone- this narrows the sitz bones, but opens the top of the pelvic bowl

  • External rotation of the femur bones as in Baddhakonasana. This also narrows the sitz bones

• For the mid-level  pelvis

  • Side lunging, with the knee out at a 45 degree angle

  • Figure 8’s with the pelvis

  • A Spinning Babies® maneuver called Side Lying Release

• For the outlet (lower pelvis)

  • Internal rotation of the femur bones (knees towards each other- not apart)

  • Hands and knees position with a cow tilt of the pelvis

  • High Squat with the tail arched backwards

Remaining active throughout your pregnancy, practicing movements such as Cat/Cow, having good general tone through the body and in the pelvic floor is another way to facilitate an open pathway through the pelvis.  Yoga, chiropractic care, and good nutrition can help promote overall body balance and health. The more balanced the body is overall, the more oiled the “lock” is, and the smoother the “key” (baby) is able to navigate through the keyhole- the pelvis. Then we can stay actively engaged in helping our babies dance their way out into our arms.

Happy birthing Mamas!

TL:DR

• The birth path through the pelvis isn’t straight, but rather curved, and the baby goes through a series of movements during birth in order to be born. These are: Engagement, Flexion, Rotation, Extension, Restitution and Expulsion.

• Moving in certain ways can help to change and open the shape of the pelvis. Certain movements can help make more space for the baby to move through and be born.

• Staying active and practicing these movements during pregnancy can make it easier to do them during the intensity of labor.

• For an animated video from nucleus medical art showing the Cardinal movements click here

• To see Bec demonstrating the cardinal movements with a model pelvis click here