What Influences Your Labor? Power, Passenger, and Passageway

When a woman goes into labor, her baby is ultimately pushed out into the world, whether through vaginal delivery or through C-section. Whichever route, it's a joyous event—one that usually requires a lot of work on the part of the mom-to-be to achieve a successful outcome.

What's the main difference between women who are able to give birth vaginally and women who deliver via C-section? The best way for me to explain the process and its variables is share with you a snappy little maxim I learned on my very first OB-GYN rounds on Labor and Delivery at (formerly) Charity Hospital.

The staff obstetrician at Charity first introduced me to the concept of "The Three Ps—Power, Passenger, and Passageway. What did he mean? Basically, that the force of labor, the size and position of the baby, and the size of the birth canal are the three main factors that contribute to any birth. How do each of these Ps play a role? Let's take a look.

Power

Labor must develop as a series of rhythmic contractions, creating what's referred to as net vector force, or a strong motion in one direction. Irregular contractions and false labor (also called Braxton-Hicks contractions) may be strong enough to become uncomfortable, but they don't effect enough of an organized force in one direction to push a baby downward and out against the cervix (the mouth of the womb). When this happens, the baby's head can't act as an effective wedge to accomplish dilatation of the cervix, the criterion used to define the beginning of labor.

Power comes into play again later in delivery if the force of labor is no longer strong. The uterus may become fatigued. Power needs to be effective enough to do its job throughout labor and up to delivery; and when it can't, a C-section is usually in order for the health of both the baby and the mom-to-be.