Complications: Cephalopelvic Disproportion
Have you ever seen a child born to a woman that made you think, There’s no way a baby that big came out of a woman that small? Cephalopelvic disproportion (CPD) is a term that is used to describe a condition in which a baby is too large to come through the mother’s pelvis. The size and shape of a woman’s pelvis varies. The position of baby often depends on the shape of mom’s pelvis, such as how wide, or how deep it is.
CPD is most often diagnosed in the second stage of labor (the pushing stage) when baby’s head fails to descend through the pelvis. It is sometimes also referred to as “failure to descend,” or “arrest of descent.” In many cases, it happens due to baby’s position, such as an occiput posterior position (face up), and baby’s body doesn’t rotate as it descends lower into mom’s pelvis.1 (It is possible, though, to deliver a baby in the occiput posterior position if mom’s pelvis is large enough.)
It may also occur if baby is not properly aligned (ascynclitic), leaning to the right or left.1
In some cases, CPD may occur if the dimensions of mom’s pelvis are too narrow. There are four different types of pelvises:
- Gynecoid, which is best suited for childbirth based on its dimensions
- Android, where the pelvis is shaped a bit like a heart
- Platypelloid, where the pelvis is broad and flat
- Anthropoid, where the inlet is oval shaped
A woman may have one of these types, or a mixture of the four.2
Measuring the pelvis
Pelvimetry refers to specific measurements in areas of a woman’s pelvis used to determine whether or not the pelvis is large enough for the woman to deliver a baby vaginally. Pelvimetry may be performed during a vaginal exam. An x-ray of the pelvis can also be performed, but it provides very little information as to whether or not a baby is too large to fit through mom’s pelvis.1
A woman’s pelvis is divided into two sections, the greater (or true) pelvis, and the lesser (or false) pelvis. It is the true pelvis that is important in childbearing.
There are three dimensions, or measurements of the true pelvis. The most important measurements of the true pelvis involve the pelvic inlet, which is the smallest part that baby’s head must pass through to react the true pelvis. If any of the measurements are smaller than normal, the pelvis may be contracted, which may make a vaginal delivery more difficult.2
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- Cunningham, F., Leveno, K., Bloom, S., Spong, C., Dashe, J., Hoffman, B., Casey, B., Sheffield, J. (2013). Abnormal Labor. In Cunningham, F., Leveno, K., Bloom, S., Spong, C., Dashe, J., Hoffman, B., Casey, B., Sheffield, J. (Eds), Williams obstetrics (24th ed.). New York, NY: McGraw-Hill
- Posner, G., Dy, J., Black, A., & Hones, G. (2013). Oxorn-Foote human labor and birth (6thed.). China: McGraw-Hill