Baby Talk | Understanding Six P's of child birth helps with labor

Q: Why do some people have their babies quickly and others seem to labor for days and days?

A: Many factors come into play to determine how long a labor will last. Basically labor length is influenced by the Six P's: passage, passenger, power, position, psyche or perception and parity.

The passage is defined as the bony boundaries of the pelvis. The shape of the pelvis determines how easily the baby can pass through. The most common pelvic shaped bone for a woman is called a gynecoid pelvis. This shaped pelvis is easiest for a baby to pass through.

However, 20 percent of women have a pelvis that may resemble an android pelvis, which is the most common pelvic shape found in males. Because the android pelvis is narrower, it is more difficult for a baby to pass through the pelvis. There are two others types of pelvises, anthropoid and platypelloid, these are rare and may cause a difficult delivery. Physical injuries to a pelvis can also alter the shape of the pelvis.

Another passage the baby must past through is the cervix, the lower portion of the uterus. Trauma to the cervix may affect its ability to open and also to affect its ability to stay closed so that a pregnancy can be completed.

Next is the passenger. The size, position, and presenting part of the baby have a major impact on the length of labor. The size of the baby has to be compatible with the size of the mother's pelvis. A common reason to do a cesarean is called CPD, cephalic (baby's head) pelvic (mom's bone) disproportion (the baby's head is too big for the mother's pelvis). I know a doctor who always calls it WCO -- won't come out!

The power factor in labor refers to the ability of the uterine muscle to contract. The uterus is an involuntary muscle. It has to not only start contracting, but it must establish a pattern of contractions. Every time the uterus contracts it pushes the baby towards the cervix. This is really what labor is all about. The contractions cause the cervix to stretch open and allow the baby into the birth canal.

Position refers to not only the position of the baby, but also the position of the mother. The old adage that what is up must come down also refers to babies. When a mother is in an upright position this contributes to abdominal wall relaxation. This helps the fundus (the upper portion of the uterus) to go forward due to the force of gravity, which then leads to the straightening of the birth canal and widening of the pelvic outlet. All of which helps a baby to be born.

The most comfortable position for a baby to be in is called the vertex, or head down position. This allows the baby's head to press against the cervix during a contraction. Causing the cervix to thin and open up to allow the baby into the birth canal.

Any other position, such as a breech (baby is upright in the uterus instead of in a down position), transverse (where the baby is laying sideways), or if the baby is presenting a hand, foot, forehead, or if the umbilical cord is presenting itself before the baby, requires a surgical, cesarean, delivery.

The mother's mental state (psyche) and her perception of what labor will be like may also affect her labor. One of the goals of childbirth education classes is prepare the expectant mother and her partner for whatever their particular childbirth experience is going to be.

No one knows exactly what their experience will be before labor begins. However, in the classes there is discussion about how labor progresses, what is normal and what is not, what to expect from yourself and your partner.

It is an opportunity to discuss any anxious feelings you may be having about labor. Excessive anxiety can interfere with labor.

Childbirth can be viewed as either a meaningful or a stressful event. Our cultural background, stories that people have told you about labor, your support system, previous birth experiences all affect a woman's psyche. Fear contributes to pain, pain leads to tension, tension affects circulation, which increases the pain, which in turn ends up increasing the fear. It can be a vicious cycle.

Last but not least there is parity. Parity refers to how many babies a woman has delivered. Typically a woman's first labor is her longest. The average length of time is anywhere from 12 to 18 hours. It is not uncommon for future labors to be shorter.

Every labor, every mother, every birth, every baby are unique. The Six P's determine the time it takes for this new person to make their birthday appearance.

Katie Powers, R.N., is a board-certified lactation consultant and perinatal educator at Manatee Memorial Hospital's Family BirthPlace. Her column appears every other week in Health. Contact her at katie.powers@mmhhs.com.

This story was originally published February 1, 2016 at 4:54 PM with the headline "Baby Talk | Understanding Six P's of child birth helps with labor ."