Umbilical cord prolapse
|Umbilical cord prolapse|
Cord prolapse, depicted by W.Smellie, 1792
|Classification and external resources|
Umbilical cord prolapse occurs when the umbilical cord comes out of the uterus with or before the presenting part of the fetus. It is a relatively rare condition and occurs in fewer than 1% of pregnancies. Cord prolapse is more common in women who have had rupture of their amniotic sac. Other risk factors include maternal or fetal factors that prevent the fetus from occupying a normal position in the maternal pelvis, such as abnormal fetal lie, too much amniotic fluid, or a premature or small fetus. The concern with cord prolapse is that pressure on the cord from the fetus will cause cord compression that compromises blood flow to the fetus. Whenever there is a sudden decrease in fetal heart rate or abnormal fetal heart tracing, umbilical cord prolapse should be considered. Due to the possibility for fetal death and other complications, umbilical cord prolapse is considered an obstetric emergency during pregnancy or labor. Current management guidelines focus on quick delivery, which usually entails a cesarean section. With appropriate management, the majority of cases have good neonatal outcomes.
There are three types of umbilical prolapse that can occur:
- overt umbilical cord prolapse: descent of the umbilical cord past the presenting fetal part. In this case, the cord is through the cervix and into or beyond the vagina. Overt umbilical cord prolapse requires rupture of membranes. This is the most common type of cord prolapse.
- occult umbilical prolapse: descent of the umbilical cord alongside the presenting fetal part, but has not advanced past the presenting fetal part. Occult umbilical prolapse can occur with both intact or ruptured membranes.
- funic (cord) presentation: presence of the umbilical cord between the presenting fetal part and fetal membranes. In this case, the cord has not passed the opening of the cervix. In funic presentation, the membranes are not yet ruptured.
Signs and symptoms
The first sign of umbilical cord prolapse is usually a sudden decrease in fetal heart rate that is severe and does not immediately resolve. On a fetal heart tracing, this would usually look like moderate to severe variable decelerations. Occasionally, the cord can be seen or felt on vaginal examination, particularly with overt cord prolapse.
Risk factors that are associated with umbilical cord prolapse tend to make it difficult for the fetus from appropriately engaging and filling the maternal pelvis or are related to abnormalities of the umbilical cord. The two major categories of risk factors are spontaneous and iatrogenic, or those that result from medical intervention.
- spontaneous factors:
- fetal malpresentation: abnormal fetal lie tends to result in space below the fetus in the maternal pelvis, which can then be occupied by the cord.
- polyhydramnios, or an abnormally high amount of amniotic fluid
- prematurity: likely related to increased chance of malpresentation and relative polyhydramnios.
- low birth weight: usually described as <2500 g at birth, though some studies will use <1500g. Etiology is likely similar to those for prematurity.
- multiple gestation, or being pregnant with more than one fetus at a given time: more likely to occur in the fetus that is not born first.
- spontaneous rupture of membranes: about half of prolapses occur within 5 minutes of membrane rupture, two-thirds within 1 hour, 95% within 24 hours.
- iatrogenic factors
Umbilical cord prolapse should always be considered a possibility when there is a sudden decrease in fetal heart rate or variable decelerations, particularly after the rupture of membranes. With overt prolapses, the diagnosis can be confirmed if the cord can be palpated on vaginal examination. Without overt prolapse, the diagnosis can only be confirmed after a cesarean section, though even then it will not always be evident at time of procedure.
The gold standard for treatment of umbilical cord prolapse in the setting of a viable pregnancy typically involves immediate delivery by the quickest and safest route possible. This usually requires cesarean section, especially if the woman is in early labor. Occasionally, vaginal delivery will be attempted if clinical judgment determines that is a safer or quicker method.
Other interventions during management of cord prolapse are typically used to decrease the chance of complications while preparations for delivery are being made. These interventions are focused on reducing pressure on the cord to prevent fetal complications from cord compression. The following maneuvers are among those used in clinical practice:
- manual elevation of the presenting fetal part 
- repositioning of the mother to be head down with feet elevated
- filling of the bladder with a foley catheter, or tube through the urethra to elevate the presenting fetal part 
- use of tocolytics (medications to suppress labor) have been proposed, usually in addition to bladder filling rather than a standalone intervention 
The primary concern with umbilical cord prolapse is inadequate blood supply, and thus oxygen, to the fetus if the cord becomes compressed. The cord can become compressed either due to mechanical pressure (usually from the presenting fetal part) or from sudden contraction of the vessels due to decreased temperatures in the vagina in comparison to the uterus. This can lead to death of the fetus or other complications.
Historically, the rate of fetal death in the setting of cord prolapse has been as high 40%. However, these estimates occurred in the context of home or births outside of the hospital. When considering cord prolapses that have occurred in inpatient labor and delivery settings, the rate drops to as low as 0-3%, though the mortality rate remains higher than for fetuses without cord prolapse. The reduction in mortality for hospital births is likely due to the ready availability of immediate cesarean section.
Many other fetal outcomes have been studied, including Apgar score (a quick assessment of a newborn's health status) at 5 minutes and length of hospitalization after delivery. While both measures are worse for newborns delivered after cord prolapse, it is unclear what effect this has in the long-term. Relatively large studies that have tried to quantify long-term effects of cord prolapse on children found that less than 1% (1 in 120 studied) suffered a major neurologic handicap, and less than 1% (110 in 16,675) had diagnosed cerebral palsy.
The incidence of umbilical cord prolapse ranges from 0.1-0.6% of all pregnancies. This rate has remained stable over time. A recent study estimates 77% of cord prolapses occur in singleton pregnancies, or those where there is only one fetus. In twin pregnancies, cord prolapses occur more frequently in the second twin to be delivered, with 9% in the first twin and 14% in the second twin.
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