Birth Injury Blog

Arrest of Descent and Cephalopelvic Disproportion (CPD)

Posted By Beam & Raymond || 24-Jul-2015

The Relationship Between CPD/Cord and Head Compression and Diminished Fetal Oxygen Reserves

Cephalopelvic disproportion (CPD) is a condition that occurs when there is a size discrepancy between the maternal pelvis and the fetal head such that the baby's head is too large to pass through the mother's pelvis. Cephalopelvic disproportion occurs when the fetal head is too large, the maternal pelvis is too small, or the fetal head is malpositioned as it enters the birth canal, presenting a significant risk to both the mother and the child. Though problematic and potentially dangerous, diagnosing cephalopelvic disproportion can be difficult in the absence of extreme circumstances such as an abnormally small maternal pelvis or macrosomia (an abnormally large child), and often times it can only be identified by abnormalities in length of labor, abnormal fetal heart tones, or the presence of molding and/or caput during labor.

Perhaps the most significant danger that cephalopelvic disproportion carries with it is the potential for compression of either the fetal head or the umbilical cord, both of which can have severe consequences for a child in labor. Though the causes of cephalopelvic disproportion vary, both of these risks are still endemic to cephalopelvic disproportion, as the passage of the fetal head through a limited space can cause compressive forces to occur to the head itself as well as potentially cause the umbilical cord to be compressed in the event that it is trapped between the fetal head and the maternal pelvis during labor. This can lead to brain damage from direct trauma or from reduction of available oxygen to the fetus.

Fetal head compression typically occurs in the event that large amount of pressure are placed on the skull during labor, and can potentially result in fetal nerve damage, skull fractures, intracranial hemorrhage, and even brain damage such as cerebral palsy. Though compression of the fetal head can occur as a result of other factors as well as in the absence of cephalopelvic disproportion, the risk is dramatically increased in the event that cephalopelvic disproportion is a known condition. Cephalopelvic disproportion presents a much higher degree of risk for fetal head compression, as the delicate fetal head must pass through a very unaccommodating maternal pelvis in addition to other potentially traumatic forces that are already present during labor.

Umbilical cord compression is another dangerous condition that is often associated with cephalopelvic disproportion, as the potential for the umbilical cord to become trapped between the fetal head or body and the maternal pelvis is greatly increased when cephalopelvic disproportion is present. Umbilical cord compression is dangerous and potentially life threatening in that it can cut off and severely deplete the baby's supply of oxygen while in utero. Prolonged compression of the umbilical cord as a result of cephalopelvic disproportion can have severe consequences, as a lack of oxygen can lead to fetal asphyxia and potentially result in hypoxic-ischemic encephalopathy, or "HIE," if the oxygen deprivation is too prolonged.

With such severe and potentially damaging risks involved, it is important the physicians take careful steps in order to determine whether cephalopelvic disproportion is present prior to attempting a vaginal delivery. Though making an exact determination of cephalopelvic disproportion may be difficult prior to delivery, there are still many steps that doctors can take to gain a sense of the special dimensions that the baby will be navigating during labor in order to paint a clearer picture of what must be done to ensure a safe delivery and a healthy child.

Ultrasonographic imaging and ultrasound examinations are both ways in which doctors can measure the size of the fetal head, and the assessment of the dimensions of the maternal pelvis through a process known as pelvimetry are important ways in which a physician may make a more accurate determination as to the existence of cephalopelvic disproportion. These steps are extremely important to take in order to protect the child, as without making efforts towards obtaining a clearer picture of what conditions the baby will face during labor, it becomes far more difficult to assure a safe delivery and healthy outcome for the child.

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