Pathway to Birth: How Your Pelvis Paves the Way for Baby's Smooth Arrival

Transformative is not enough to describe what is happening in a birthing body.

But that’s what I’ll go with today. One of the most significant areas of change occurs in the pelvis, which must adapt in so many ways to create the path of least resistance for the baby during birth. Today, we’ll dive into ten key ways the pelvis prepares for this remarkable journey, ensuring a smoother delivery.

1. Pelvic Mobility: Creating Space for Baby’s Descent

During pregnancy, the pelvis undergoes a process of increased mobility (yay relaxin!) to accommodate the growing baby make birth a little easier. The pelvic joints, especially the sacroiliac joints and the pubic symphysis, become more flexible. This enhanced mobility is crucial for allowing the pelvis to widen and adapt as the baby moves down into the birth canal (why do we call it the birth canal?? It’s the vagina… I’m talking about the baby moving out of the uterus into the vagina).

Dr. Emily hold a model of a pelvis in her hand as she gazes lovingly at the rectum, uterus, and bladder which are all attached ... similar to how they exist in the body- though in the body they should glide easily over one another, and not be adhered fascially. 

2. Relaxation of Ligaments: Hormonal Help for Flexibility

You may be wondering if that hormone I mentioned above, relaxin, is a real thing. It is! Relaxin plays a pivotal role in preparing the pelvis for birth. It softens and relaxes the ligaments around the pelvic joints, making them more pliable-wild that it can target this area of the body, but it has been shown to be true. Specifically, the -relaxation- is most noticeable in the sacroiliac joint, pubic symphysis, and sacrococcygeal joint. By increasing flexibility, relaxin ensures that the pelvis can expand and accommodate the baby’s passage during labor… Remember, even micro-millimeters make a difference.

3. Widening of the Pelvic Outlet: Making Room for Baby

As labor progresses and the baby descends, the pelvic outlet—the lower opening of the pelvis—needs to widen. This is achieved through the opening of the sacroiliac joints and the forward tilt of the sacrum, the triangular bone at the base of the spine. This widening is essential for providing enough space for the baby to pass through the birth canal. PRO TIP: I talk a lot about how internal hip rotation can assist with this. Ask me how!

4. Engagement of the Fetal Head: Finding the Path

One of the most critical steps in labor is the engagement of the baby’s head in the pelvic inlet, the upper opening of the pelvis. Ideally, the baby’s head engages in an occiput anterior position, where the back of the baby’s head is facing the mother’s front. This alignment allows the baby’s head to fit into the widest part of the mother’s pelvis, ensuring a smoother descent.

5. Anterior Pelvic Tilt: Aligning for Success

A very slight anterior tilt of the pelvis during pregnancy is beneficial for aligning the uterus and baby with the pelvic inlet. Or at least NOT a posterior tilt like we are all want to do… on the couch, at our desks, doing dishes….. This position of the pelvis helps the baby to settle into an optimal position, promoting an efficient and effective descent through the birth canal. The anterior tilt also supports the natural curve of the spine, reducing strain and discomfort for the mother. (And helps you not lose your glutes as bad)

6. Flexion of the Coccyx: Opening the Exit

The coccyx, or tailbone, plays a small but vital role in birth. [Had any past coccygeal injuries? You should talk to me about pelvic floor PT as it may affect your birth!] As the baby moves through the birth canal, the coccyx needs to flex backward (extend? I don’t know- come at me fellow PTs) to create more space in the pelvic outlet. This backward movement, facilitated by the relaxation of the surrounding ligaments, allows the baby’s head to pass through with less resistance, making crowing happen with a little more ease.

7. Optimal Muscle Tone: Balancing Strength and Flexibility

The muscles of the pelvic floor are essential for supporting the baby during pregnancy and allowing for a smooth delivery. During labor, these muscles need to have an optimal tone—neither too tight nor too loose. Goldilocks tone! Balanced muscle tone ensures that the pelvic floor can support the baby’s descent while also allowing for the necessary stretch and relaxation as the baby crowns.

8. Rotation and Descent: Navigating the Pelvic Diameters

As the baby moves through the pelvis, it must rotate and descend through various diameters of the pelvic inlet, midpelvis, and outlet. This rotation is a natural part of the birthing process, with the baby’s head turning to fit through each section of the pelvis. (YES- your baby is an extremely active participant in birth- you should think of it as something you are doing TOGETHER). Your pelvis must allow for these rotational movements, adapting to the baby’s position and facilitating a smoother passage.

9. Adaptation to Fetal Positioning: Embracing Asymmetry

Not all babies are perfectly aligned during labor, and that’s okay. The pelvis is designed to adapt to the baby’s positioning, allowing for asymmetrical movements if necessary. Whether the baby’s head is slightly tilted or rotated, the pelvis can adjust to accommodate these variations, ensuring that the baby still finds the path of least resistance. And if that isn’t working, hopefully you have worked with me throughout pregnancy, so you KNOW what tools to use to make small changes to your pelvis during birth!

10. Pelvic Floor Relaxation: Easing Baby’s Exit

Finally, the relaxation of the pelvic floor muscles is crucial during the final stages of labor. These muscles, including the levator ani, need to relax sufficiently to allow the baby’s head to crown and pass through the birth canal. Proper relaxation of the pelvic floor reduces resistance and minimizes the risk of tearing, making the birthing process smoother and less traumatic for both you and baby.

PHEW!

That was a lot of information, but understanding how the pelvis changes during pregnancy to adapt for birth can empower birthing bodies with knowledge about the changes they are undergoing- and the incredible adaptations that occur to facilitate birth. These transformations are nature’s way of ensuring that both mother and baby are as prepared as possible for the journey ahead.