Cephalopelvic Disproportion (CPD): Causes and Diagnosis
Cephalopelvic disproportion (CPD) occurs when a baby’s head or body is too large to fit through the mother’s pelvis. It is believed that true CPD is rare, but many cases of “failure to progress” during labor are given a diagnosis of CPD. When an accurate diagnosis of CPD has been made, the safest type of delivery for mother and baby is a cesarean.
What causes cephalopelvic disproportion (CPD)?
Possible causes of cephalopelvic disproportion (CPD) include:
- Large baby due to:
- Hereditary factors
- Postmaturity (still pregnant after due date has passed)
- Multiparity (not the first pregnancy)
- Abnormal fetal positions
- Small pelvis
- Abnormally shaped pelvis
How is cephalopelvic disproportion (CPD) diagnosed?
The diagnosis of cephalopelvic disproportion is often used when labor progress is not sufficient and medical therapy such as use of oxytocin is not successful or not attempted. CPD can rarely be diagnosed before labor begins if the baby is thought to be large or the mother’s pelvis is known to be small.
During labor, the baby’s head molds and the pelvis joints spread, creating more room for the baby to pass through the pelvis.
Ultrasound is used in estimating fetal size but not totally reliable for determining fetal weight. A physical examination that measures pelvic size can often be the most accurate method for diagnosing CPD. If a true diagnosis of CPD cannot be made, oxytocin is often administered to help labor progression. Alternatively, the fetal position is changed.
What about future pregnancies?
Cephalopelvic disproportion is rare. According to the American College of Nurse Midwives (ACNM), CPD occurs in 1 out of 250 pregnancies. If you have been diagnosed with CPD, it does not mean that you will have this problem in future deliveries.
According to a study published by the American Journal of Public Health, more than 65% of women who had been diagnosed with CPD in earlier pregnancies were able to deliver vaginally in subsequent pregnancies.
Compiled using information from the following sources:
Danforth’s Obstetrics and Gynecology Ninth Ed. Scott, James R., et al, Ch. 22.
American College of Nurse-Midwives, https://www.acnm.org/