Definition

Cephalopelvic Disproportion (CPD) is a condition where the baby's head or body is too large to pass through the mother's pelvis. According to the American College of Nurse-Midwives (ACNM), CPD occurs in 1 out of 250 pregnancies, indicating that CPD is actually rare.

CPD is often diagnosed when labor fails to progress, the cervix stops dilating, or the baby does not descend through the pelvis. However, this can also be caused by other factors, such as the baby's body or head position, which complicates delivery. This condition can cause obstructed labor and is sometimes misinterpreted as CPD.

Causes

Several factors can cause CPD, including:

• Large baby size: This can be due to:
• Genetic factors
• Diabetes
• Postmature pregnancy (gestational age beyond 42 weeks)
• Abnormal fetal position
• Narrow pelvis
• Abnormal pelvic shape

Most women, including those with small bodies, can deliver normal-sized babies, even if the doctor says the baby is large. The pelvis is a flexible cavity that can facilitate delivery, and the baby's skull bones are designed to mold for passage through the birth canal.

Therefore, if your doctor tells you that your baby is large, there are a few things to understand: the doctor cannot weigh the baby or know the exact size of the baby's head while still in your body. Ultrasound is a useful tool and can give doctors an estimate of the fetus's size, but it remains an approximation. Often, babies who appear large on ultrasound are born with average weights.

Only about 10% of deliveries result in babies who are truly very large, with birth weights over 4 kg, meaning about 90% of babies are not excessively large.

If a mother has had pelvic injuries or genetic issues that cause a narrow pelvis, or if the baby's position is not ideal for delivery, CPD can be a problem.

Risk Factor

 Although CPD is rare, certain situations and conditions can increase the risk. Some risk factors for CPD include:

• Fetal risk:
• A larger-than-average baby, especially if the weight exceeds 4 kg, and even more so if it exceeds 4.5 kg.
• If the lowest part of the fetus is the buttocks or feet, or if the baby is transverse, affecting the labor process.
• Labor is easier when the smallest part of the baby's head (the anterior fontanelle) faces the birth canal. If other parts of the head, such as the forehead or face, enter the birth canal first, it will be more difficult to pass through the mother's pelvis.
• Some health conditions in the baby, such as hydrocephalus, can cause the baby's head to be larger than average.
• Gender: Male babies tend to be larger than females, slightly increasing the risk of CPD in male babies.

• Maternal risk:
• History of pelvic surgery or injury
• Narrow or abnormally shaped pelvis
• First pregnancy
• Diabetes and gestational diabetes
• Polyhydramnios (excess amniotic fluid)
• Obesity
• Malnutrition
• History of fertility treatments
• Postmature pregnancy (beyond the due date)
• History of cesarean section
• Short stature
• Hispanic descent
• Teenage pregnancy where the pelvic bones have not fully developed

Diagnosis

CPD is often diagnosed when labor does not progress as it should and medical interventions like oxytocin are unsuccessful. CPD can sometimes be diagnosed before labor begins if the baby appears large and the mother's pelvis appears small.

During labor, the baby's head will mold, and the pelvic joints will widen, creating more space for the baby to pass through the pelvis.

Ultrasound is used to estimate the baby's size. However, this examination is not 100% accurate in determining fetal weight. Physical examination measuring pelvic size often provides accurate results in diagnosing CPD.

Management

Doctors will use medications like oxytocin to induce labor as the first response to labor not progressing normally. In cases like shoulder dystocia (where the baby's shoulders cannot be delivered), doctors may use tools like forceps or vacuum extractors to reposition and assist the baby's birth.

However, in true CPD, the baby's chances of passing through the mother's pelvis are very small. Therefore, doctors need to quickly recognize fetal distress and obstructed labor so that a cesarean section can be performed to prevent serious injury to the baby. Repeated attempts to deliver the baby normally, prolonging labor, are dangerous.

Complications

Complications of CPD include:

• Premature rupture of membranes (before labor)
• Shoulder dystocia
• Extreme compression of the baby's head
• Umbilical cord prolapse
• Fetal distress
• Damage to the mother's perineum (area between the anus and vagina)
• Baby's head injury
• Uterine rupture
• Postpartum hemorrhage

Most women with CPD will have a successful delivery via cesarean section. There is no evidence that CPD affects the baby after birth. Statistics show that about 1 in 3 cesarean sections are performed due to suspected CPD.

Other studies published in the American Journal of Public Health show that 65% of women diagnosed with CPD in a previous pregnancy can deliver normally in subsequent pregnancies, even with larger babies than the previous CPD-suspected pregnancy. This means that even if you were diagnosed with CPD, it does not mean you will have this problem in future pregnancies.

Prevention

CPD is usually not diagnosed until labor problems occur, making it difficult to prevent. However, doctors will examine and monitor your pregnancy. If CPD is suspected, doctors will discuss this with you, including delivery options.

Doctors will evaluate CPD by:

• Asking about your medical history, including family history, and any previous surgeries or injuries
• Examining the pelvis to determine its size and shape
• Using ultrasound and physical examination to estimate the baby's size
• Monitoring the fetus's position in the womb

When to See a Doctor?

If you are pregnant, it is advisable to have regular prenatal check-ups so that the doctor can examine and monitor you and your fetus. If you have had CPD in a previous pregnancy, inform your doctor so they can be better prepared to develop a delivery plan to prevent complications during the upcoming delivery.

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