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Optimal Fetal Positioning: How Baby’s Position Can Alter Your Labor

By Amy Michaelson

The words “Optimal Fetal Positioning” may sound like technical jargon, but to my ears they are the sound of hope and relief. While my beliefs about birth are mostly rooted around the ideas of keeping hands off the pregnant mama and letting her and the baby inside do their work, understanding the way our bodies were designed can lend an enormous amount of insight into what makes labor work, and what gets in its way.

When dealing with optimal fetal positioning, we mainly focus on two parts of the participating bodies: the mother’s pelvis and the baby’s head. Of course, these body parts do not function on their own, and are intricately connected to the entire rest of the body. But let’s start by looking at these two parts so that we can have a better understanding for how birth works.

The Pelvis

The pelvis is a complex and dynamic set of bones. It cannot be defined by one shape or size. It is both wide and narrow, short and long—and it can alter its shape! What is so wonderful about all of this, is that babies’ heads and bodies are able to maneuver their way through the various turns and twists of the pelvis, and still find their way out.

Pelvic Diameters

There are different types and shapes to pelvises among humans, but they all have the same basic structure: the inlet, the cavity and the outlet. The diameters of each of these parts of the pelvis differ significantly.

The inlet of the pelvis is about 11 to 12 cm, front to back, and 13 to 13.5 cm across. The pelvic cavity is the narrower part of the pelvis. It is rounder, about 12 cm in diameter.

The pelvic outlet is narrower side to side than it is front to back. The amazing thing about the pelvic outlet is that the joints that hold the lower pelvic bones together are quite flexible. If a mama is allowed to be upright, and baby is able to press its way through, the tailbone (sacrum and coccyx) is able to move freely and will open up as the baby’s head comes through the pelvis, creating additional space.

The Fetal Head

As with the maternal pelvis, the fetal head is made up of various mobile bones that form a variety of shapes and sizes. Because babies’ heads move in different directions, both on their bodies, and in relation to the mother’s pelvis, I’m going to break down the different ways we describe the fetal head.

The first aspect of the baby’s head position to consider is its attitude. Attitude is a term that describes the amount of flexion or extension of the baby’s head, or how tucked the baby’s chin is. Why is flexion important? The amount of flexion present will alter the dimensions of the baby’s head as it moves through the pelvis, cervix, and vagina. A cervix opens only as far as it needs to fit around the baby’s head. If the head diameter is small, it will only need to dilate that amount. If the diameter is larger, more dilation will be necessary. A well-flexed head is when a baby’s chin is tucked well into its chest, with the occipital bone (in back of the head) presenting first. There are varying degrees of flexion and extension.

1. Complete Flexion: This is the optimal position for a baby’s head to be in. The angle of the head and neck are less than 90 degrees, meaning baby’s chin is tucked well into its chest, and the very back of the head presents first.

2. Moderate Flexion, or Military Attitude: With the military attitude, the baby’s head and neck are at a 90 degree angle, as if the baby is looking straight forward.

3. Extended, or Brow Presentation: This attitude has the baby’s head tilted back a bit, the angle of the head to the neck greater than 90 degrees.

4. Hyperextended, or Face/Chin Presentation: This attitude has the baby’s head tilted way back and can be referred to as “star gazing.”

The diameter of the fetal head varies greatly in relation to how well flexed it is.

Fetal Head Bones/Molding

So, can an unflexed head still fit through the pelvis and birth canal? Although it often takes more time and effort, yes, an unflexed head can still fit through.

What if the baby comes down in one of those suboptimal positions, or what if the baby really does have a large head? The wonderful thing is, we were designed to deal with this as well. Just as the maternal pelvis can expand to allow more room, the fetal head can contract to take up less room.

The adult human skull has a static shape. It doesn’t change unless the bones are broken. But in fetuses and children up to 8 years old, the sutures between these bones of the skull have not yet fused. These unfused bones and the fontanels, or small gaps, between the bones, create a skull with the ability to shift, bones overlapping bones, reducing the diameter of the skull. This ability can even allow a malpositioned baby to fit through his mother’s pelvis. It amazes me that we are able to adapt so well. Vaginal birth is very accommodating!

Fetal Head Position

Fetal head position is different than the attitude of the head. The attitude deals with tilting the head up and down from the neck. Position deals with the direction in which the head (and the body that follows) is facing.

When discussing fetal head position, the occipital bone— the one at the very back of the head—is always what is used as the point of reference. We describe the fetal head position by the direction the fetal occipital bone is pointing toward.

The mother’s front portion is called the anterior. Her sides are called transverse. And her back portion is called the posterior. So, if the baby’s occiput is pointing toward the front of the mother, the baby is in an “occiput anterior” position. If pointing slightly to the left, it is described as “left occiput anterior.”

The various fetal head positions are as follows:

  • ROA — right occiput anterior

  • ROT — right occiput transverse

  • ROP — right occipital posterior

  • OP — occiput posterior

  • LOP — left occiput posterior

  • LOT — left occiput transverse

  • LOA — left occiput anterior

  • OA — occiput anterior

Putting the Pieces Together

Cardinal Movements: The way a baby moves through the mother’s pelvis on its exit from the womb is described as the “cardinal movements.” The cardinal movements normally begin with the fetal head in the LOA position. The reason why LOA is the most described starting position is as follows. As the baby enters the inlet of the pelvis, the widest diameter is transverse—from side to side. But the baby’s head, whether flexed well or not, will be wider front to back. So, the best way for the baby’s head to enter the pelvis is in a sideways, or OT position.

Internal Rotation: As the baby is pushed further into the pelvis by the power of the contractions and enters the pelvic cavity, the dimensions change. The cavity is more equally rounded, and since body movements tend to move in a clockwise direction, the baby is rotated from LOT to LOA.

Extension: The pelvic cavity is where head flexion really has a big impact. A well-flexed head will have a much more successful journey past this narrow section than an extended head. As the baby moves through the cavity, it will continue its rotation to OA.

Emerging: Once the baby has moved through the pelvic cavity, the front part of the pelvis and pubic arch is no longer pushing against the occiput. But the sacrum and coccyx at the back are still creating a posterior resistance. The pelvic outlet is wider from front to back than from side to side. And if mom is in a position that allows free movement of the sacrum and coccyx (side-lying, hands and knees, upright/ squat), the front-to-back opening will be even greater as the baby pushes against the sacrum and coccyx. This anteroposterior opening creates a space that favors an OA position for the baby’s head.

Crowning: As the baby’s head moves through the pelvic cavity, and under the pubic arch, we see the baby start to crown. Through the pelvis the baby has rotated from LOT to OA, and when the baby’s head is born, the baby is usually looking toward mom’s back.

External Rotation/Restitution: The baby’s head has already gone on its internal rotational journey. As the head emerges, the shoulders follow with their own rotations. The shoulders enter the pelvis side to side, because it is widest that way. As the shoulders move through the tight pelvic cavity, the body spins clockwise.

The rotation continues until the shoulders are front to back, this being the widest measurement of the pelvic outlet. On the outside you’ll see the baby’s head and occiput turn toward the mother’s right leg. Because of the pubic arch, the anterior shoulder will emerge first, followed by the posterior shoulder. The baby usually continues rotating until it’s facing forward as the rest of the body is born.

Backing Up

What I’ve just described is the best way that a baby fits through the twists and turns of the maternal pelvis. The two are designed to work together in this manner, allowing the baby and the mother to remain intact. Getting a baby into this starting position is what optimal fetal positioning is all about.

Inside the body, there’s a certain phenomenon that takes place called dextrorotation: The body has a tendency to have its processes move in a clockwise direction. Our uteri move the same way. As the uterus contracts and releases, babies are turned in a clockwise manner. If a baby were to start out in an ROA position (baby’s occiput aligned closer to mom’s right hand position), this would mean that the baby would need to rotate a full circle, all the way from ROA to ROT to ROP to OP to LOP to LOT to LOA, in order to get to the ideal OA position for birth. That’s quite a long journey, and includes a considerable length of time moving against the sacrum and coccyx, which can be extra painful for many mothers. Starting out in the LOA position means that the uterus can focus on pulling open the cervix and moving the baby down, instead of also working on turning the baby full circle into another position.

Optimal Fetal Positioning During Pregnancy

I would say that the majority of “failure to progress” babies are due to malpositioning, and that the majority of the malpositioning is due to our modern lifestyles. Instead of walking to travel, we slouch in our cars. We do not sit cross-legged on the floor, or squat—we lounge on sofas and in easy chairs. Most of our work is done while seated, and most of us sit poorly. So, watch your posture! Some of us may need more help than just normal posturing to get our babies to move into more favorable positions. Perhaps you had a bad fall when you were a kid. Maybe you were in a car accident. Or you played soccer and made the same one-sided twisting motion over and over again. All of these things can affect pelvis alignment and the uterine ligaments.

When the pelvis is bumped out of alignment, or the uterine ligaments are tighter on one side than the other, there will be a twist in the uterus. While a slight twist or misalignment may seem like a minimal problem from the outside, everything is magnified on the inside. A slight twist outside turns into a large twist on the inside, making rotation more difficult for the baby.

Chiropractic care is wonderful for dealing with these bone and ligament issues. Mayan Abdominal Massage and Rybozo have also been used to get the body into better alignment. In pregnancy and birth, we want the body to open up—letting the pelvis open and move, and the ligaments stretch. So, to help a baby be able to move, you need to move! (Visit spinningbabies.com for some great exercises.) Many of the techniques for optimal fetal positioning during pregnancy can also be applied during labor. While it’s best for the baby to be in an optimal position prior to the onset of labor, sometimes it cannot be helped.

Optimal fetal positioning is a wonderful skill to know, whether you are the pregnant mother, a doula, a nurse, midwife, or doctor! Knowing the ins and outs of fetal positioning may mean the difference in a vaginal or a cesarean birth. It may mean the difference between a 12-hour labor and a 48-hour labor. It may mean the difference between an extremely intense back labor or a labor that is more manageable.

Knowing how to make the difference is an invaluable skill to have! While there are ways to help give a baby the opportunity to rotate into an optimal fetal position, it is important to remember that pelvises and babies’ heads are still amazing at adapting. Babies can still be born in posterior positions, with brow and face presentations, and in other “non-optimal” positions. It may take a little more time, and a lot more effort, but the human body is amazing at making birth work.