Force & Yield: A New View On The Uterus In Labor

When it comes to the uterus, the obstetric model suffers from tunnel vision.  The suggested solution for so many problems is: more force, more power, more contractions.  While we honor the powers of the uterus, we also understand that birth does not just happen through contractions, but also the spaces in between.  Birth is not like squeezing toothpaste out of a tube; it is pulsatile and wavelike…coming and going and coming and going.  In my own labor, for example, I experienced my contractions first in my mouth (no, seriously), like a tingling sensation, before they surged in my uterus.  I knew by that sensation that another wave was coming.  So in those waves, birth is not just a process of force, it is also a process of yield, and the ebb-and-flow between them.

Obstetrics is entirely focused on fundal dominance and progress through power and force.  Naturally, if the view of how birth happens is predicated on the principle of increasing power and force, the solutions will be too. And thus we find ourselves starting Pit on a grand multip who is breathing well through her contractions at 8 centimeters because someone wants to “move things along.”

Life, labor, and uterine contractions – none of these are linear!  So, we expand our view.

Force and yield create progress

The uterus doesn’t contract like a bicep. It behaves more like a hydraulic, self-coordinating organ. There are three muscle layers of myometrium, richly vascular, and interwoven with connective tissue, lymphatics, and extracellular matrix. Uterine contractions move fluid as well as tissue, which creates pressure waves, not just shortening: contraction + relaxation = fluid movement + force transmission. Let that sink in.  Contraction + relaxation = fluid movement + force transmission.  The uterus changes shape over time, not just moment-to-moment.

Within the uterus, there is a gradient of muscle thickness from top to bottom.  Muscle cells are surrounded by a scaffolding of collagen.  Collagen determines how much tissue can change. Old school scientists dissected muscle cells, not realizing that they were ignoring the surrounding tissues — which are a major factor in contractility.  During labor, both the cervix and the uterus lose collagen. Samples taken from elective cesareans show much more collagen than a cesarean after laboring.  There is also a reverse gradient from the cervix up to the fundus, in terms of collagen levels.  In fact, cervical collagen is one of the factors considered in a Bishop score. A ‘ripe’ cervix means the collagen has been absorbed, making it much more changeable.

I am fascinated by Margaret Jowitt’s assertion that collagen acts as a “straitjacket” for the uterus.  Once the collagen starts melting away, labor progress ramps up.  She asserts fetal monitoring straps create tension right where we want stretch, right where the baby’s arms are, limiting movement.  Huh!

Fundal dominance also ignores the baby entirely.

Philip Steer, a pioneer of electronic fetal monitoring said in a 2023 BJOG debate that the fetus initiates contractions. They kick and the uterus responds. The baby is not a passive passenger in the process; they are an active participant in getting themselves born.  The uterus responds to the baby, and the baby responds to the uterus—a dynamic conversation, not a one-way process.  Contractions are not imposed on the baby; they are part of an interaction.  Rotation and descent are not just driven by force, but by the availability of space.  A baby cannot rotate through resistance. We’ve all seen labor pick up after a shift in space or environment or fetal position.

Fundal dominance ignores the whole person

A birthing woman is not just a uterus, she is a whole person.  

When the entire focus is on the success or failure of the uterus’ ability to contract adequately, we majorly miss the mark.  There are other significant factors that contribute to labor progress: interplay of hormones, sense of safety or threat, and impact on the nervous system.  Safety and threat are, of course, always in the eye of the beholder. I have seen plenty of labors slow or stop entirely after a distinctly threatening event.  

Assess how force is moving, not just how strong it is

If contractions are waves (and not just pressure events), then we want to start thinking about not just how strong it is, but how it travels through the body.  Remembering the anatomy as a tensegral structure – meaning it’s allllll connected – a restriction anywhere in the system could alter how the force of the contraction is able to move through. Perhaps then, a stalled labor is not just a lack of contraction power, but contraction distribution.  What is the solution, then?  It comes in the form of touch, body balancing, movement, and repositioning.

A new view…

A stalled labor may not be a failure of force, but a failure of yield.  Instead of going automatically to “Do we need to start some Pit?”, let’s think: Where is the resistance? What needs to soften? What needs to yield?  The change is not just what we do, but what we are looking for.  Force without yield meets resistance, and yield without force lacks direction.  Know which is needed, and when, is the art of supporting birth.