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Cephalopelvic Disproportion: Signs, Causes, and Potential Risks

It can seem like a miracle that a baby can fit through a woman’s pelvis during childbirth. Although about 70 percent of all deliveries are vaginal, sometimes the baby’s head is too large to pass through the birth canal. This is called cephalopelvic disproportion. Learn the signs, causes, and potential risks of this rare condition.

Cephalopelvic disproportion

A woman’s pelvis is designed to expand during pregnancy and delivery. In some cases, the baby’s head might be too large to fit through the ischial spines — the bones at the narrowest point in a woman’s pelvis — for normal vaginal delivery.

Cephalopelvic disproportion means that there is a disproportion between the baby’s head size and mother’s pelvis size. Cephalopelvic disproportion, or CPD, is a relatively rare condition that is diagnosed only during labor. 

One of the most common signs of cephalopelvic disproportion is prolonged labor or failure of progress. This means that even though there are contractions, the fetus isn’t descending and/or the cervix isn’t dilating. 

Unless your doctor identifies that you have cephalopelvic disproportion risk factors, it is unlikely that you would be diagnosed with the condition before you go into labor. However, it’s possible that your doctor might notice an abnormal fetal position or that your baby is larger than average during a routine prenatal checkup.

One of the most common signs of cephalopelvic disproportion is prolonged labor or failure of progress.

In this case, your doctor might recommend trying to reposition the baby before your due date or scheduling a C-section to avoid the potential risks related to cephalopelvic disproportion during labor. But in most cases, you will most probably be offered trial labor, where the doctor closely monitors your labor progress to see if delivery can happen vaginally and safely.

Now that you know the cephalopelvic disproportion signs and symptoms, you might be wondering what causes the condition. 

Cephalopelvic disproportion can occur when a woman’s anatomy doesn’t match the size of her baby’s head through the birth canal due to a contracted or abnormally shaped pelvis. This can be caused by genetics or as a result of rickets, pelvic tumors, or a previous injury or accident.

If CPD isn’t due to the size or shape of a woman’s pelvis, some cephalopelvic disproportion risk factors can include:

  • Gestational diabetes, which can lead to increased birth size or weight
  • Postmaturity (being pregnant after the anticipated due date, past the third trimester), which can mean that the baby grows larger than normal 
  • The position of the fetus 
  • Hereditary conditions that can cause the baby to be larger than average

Your doctor may try to mitigate some of these risks by inducing labor or changing the position of the fetus, if possible.

CPD is typically only diagnosed during labor. If labor is ineffective and there has been little or no progress even after medical interventions, the doctor may diagnose CPD.

If the doctor diagnoses cephalopelvic disproportion, they’ll likely recommend that the baby be delivered by cesarean section. Cesarean sections are the safest method of delivery for both mother and baby in cases of CPD.

A baby with cephalopelvic disproportion

The risks or complications associated with CPD are related to the dangers of obstructed labor, prolonged labor, and failure to progress. These can result in:

  • Birth injury
  • Head trauma
  • Shoulder dystocia (when the baby’s head passes through, but their shoulders get stuck)
  • Increased risk of stillbirth

For the mother, obstructed labor due to cephalopelvic disproportion could cause serious complications, including:

  • Infections of the uterus, bladder, or vaginal walls
  • Trauma to the bladder or rectum
  • Ruptured uterus, which can cause a hemorrhage, shock, or death

Cephalopelvic disproportion is the leading cause of obstructed labor. Without proper medical intervention, obstructed labor can lead to maternal death or long-term disability.

If CPD is identified early enough and appropriate action is taken (undergoing a C-section to deliver the baby), there is no evidence to suggest that CPD has any negative health impacts to the mother or baby.

If you had cephalopelvic disproportion once, does that mean you’ll always have it for future pregnancies? In most cases, women who had CPD in their first pregnancy can still give birth vaginally in later pregnancies.

Cephalopelvic disproportion is a rare condition that can lead to obstructed labor. Although CPD is diagnosed only during labor, you may still want to speak with your doctor if you have any of the associated risk factors and are concerned about your ability to deliver vaginally.

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