Human labor is miraculous. After 40 weeks of pregnancy, the uterus simply begins to contract and, some hours later, a baby is born. The woman is unable to voluntarily control the onset of labor, the strength of the contractions, or how often they occur. Essentially the uterus appears to have a mind of its own. Once started in earnest (that is, not counting any “false labor”) it is almost impossible to stop.
A major controversy exists among clinicians and scientists about how the uterus coordinates the muscular contractions in all its parts, or regions. The pregnant uterus and the brain are the only two remaining organs in the human body where there is scientific disagreement on how they actually work.
For the uterus, this lack of understanding is fairly surprising. The uterus is primarily composed of only one type of cell – the smooth muscle cell – which is responsible for creating uterine contractions. Other than sensory nerves, there are no nerves that control the contractions like with skeletal muscle, and no special pathways for signaling like with the heart. There are a variety of ways to link together the billion smooth muscle cells and visualize how they can be made to contract at the same time. But whenever researchers have investigated these mechanisms of communication, the experimental data never fully agreed with the theory.
This lack of understanding has probably contributed to our inability to precisely control labor, and without control, unfortunate outcomes occur too often. Borne is particularly concerned about our inability to stop preterm labor, and our inability to fully understand dysfunctional labor that leads to Cesarean Section deliveries. Clearly, a better understanding of how the uterus contracts is required.
Recently one of our collaborators, Dr. Roger Young, proposed a new mechanism of function for the uterus that seems to accommodate the historical and modern data. This “mechanism” actually combines two separate mechanisms, and is therefore called the “Dual mechanism”. It combines an electrical mechanism, which is used by the heart, with a much lesser-known mechanism called mechanotransduction. Mechanotransduction simply means that mechanical movement, or pressure, causes the muscle to transition from relaxed to contracted.
The key element of understanding of this research was that the pregnant uterus is fluid-filled and pressurized. Because of the pressure, each region of the uterus experiences a mechanical tension that is shared with all the other regions. This hydraulic-mechanical signaling allows the regions of the uterus to rapidly communicate with each other, much like the brakes on each wheel of your car can be activated at the same time by foot pressure at a remote location.
While the Dual mechanism is simple to describe, it took 5 years of dedicated research for the scientific community to begin to accept this as important for uterine functioning. Further work needs to be performed to establish important details of the Dual mechanism, specifically pointed towards stopping preterm labor and normalizing dysfunctional labor. However, with this new framework for uterine function, it now seems possible to understand the enigma of human labor.
With this new understanding, Borne has high hopes that additional research will find new clinical treatments. Continuing to improve understanding is the only way to gain better control of labor, so that someday soon the word “impossible” can be removed from the practice of clinical obstetrics.