What is the Birth Canal?

It’s amazing how often a term can be used without it being clearly defined. An example of this is the term birth canal, which is frequently discussed in articles on childbirth. People might read statements like: “In stage two the baby passes through the birth canal,” and it’s automatically assumed the reader will understand this statement. Yet many people don’t understand it, and there’s some variation that might make it more confusing. To clarify, the birth canal is normally defined as the passage between uterus and the outside of the vagina, but usually this only used when a woman is in labor.

The cervix or the end point of the uterus though which the baby emerges may be considered as part of the canal, although others state that the vagina is truly the only part of the birth canal. During the first stage of labor, the cervix opens to ten centimeters (3.94 inches) so that the baby can exit the uterus. This leaves the baby in the vagina, which under ordinary circumstances does not look like it would be wide or long enough to contain an entire baby. However, the vagina has remarkable properties of elasticity, and though this is painful, it really can stretch to accommodate an entire baby.

There are muscles in the canal which help a woman do the work of pushing a baby out of the vagina and out of her body. Without this ability to push, the baby wouldn’t necessarily proceed out into the world and some form of extraction, like forceps or suction could be necessary, or a cesarean section might be required. In many cases though, when women use these muscles, which feels similar to having a bowel movement, they are able to help move the baby out of the birth canal.

Even the opening of the vagina, is designed to stretch to accommodate the emerging baby’s head. However it is not uncommon for the opening to tear, and some women have a small procedure called an episiotomy, which cuts a wider opening from the base of the vagina opening into the perineum (or toward the hole in the rectum), to accommodate the babies passage out of the birth canal. This is stitched up after childbirth occurs.

Just as the birth canal is built to stretch widely for a baby, babies are a built to get through this perilous passage. One of the reasons infants have soft spots on their heads is so that their heads can be squeezed as they make it through the canal. Taking too long to pass through the canal, which isn’t uncommon especially with first time moms unaccustomed to pushing, can lead to molding of the head, and some infants may have pointy heads (temporarily) after making it through the birth canal, or some can have bumps or bruises. Though both the mother and the baby are essentially designed for this experience, it is still not an easy one.