The average umbilical cord is typically no longer than 24 inches (61 cm), so cords that exceed this length might result in problems during pregnancy or childbirth. Most problems stemming from an overly long umbilical cord are not discovered until after the birth, because it can be difficult to see this type of issue during an ultrasound. One of the most common complications of a long umbilical cord is entanglement, because the cord might become wrapped around different fetal body parts. Longer cords also have a higher risk of knots forming, which can cut off the unborn baby's oxygen supply. Additionally, a long cord increases the risk of umbilical cord prolapse, in which the cord starts to exit the uterus during pregnancy, reducing the unborn baby's oxygen supply.
In most cases of entanglement, the overly long umbilical cord is wrapped around the neck of the fetus. This could be a serious problem during birth because the baby cannot take a breath when the cord is wrapped tightly around his or her neck, but a cesarean section usually solves this issue, preventing any damage. In rare cases, the cord becomes wrapped around a fetal leg, arm or other body part, but this usually does not result in long-lasting damage. In general, the only time that a baby might suffer long-term damage or even die from this issue is when the cord is wrapped tightly around the neck during a vaginal birth, because the oxygen supply is cut off.
In some cases, knots might form in an overly long umbilical cord, especially when the fetus moves around a lot. Loose knots rarely result in any issues during pregnancy, but knots that are pulled tight might cut off the unborn baby's oxygen supply. Doctors can often detect and monitor this issue during childbirth, because the fetal heart rate might become abnormal, prompting a cesarean delivery to prevent stillbirth. During the pregnancy, however, it can be difficult to spot this problem, which is why it is one of the many causes of fetal death.
Umbilical cord prolapse describes a situation in which the cord falls from the uterus into the vagina after the water breaks but before the baby is in the birth canal. The result is that the baby often puts pressure on the cord as he or she enters the birth canal to be born, cutting off the blood supply and the oxygen that comes with it. As long as doctors detect this issue quickly, they can perform a cesarean section to relieve the pressure of the baby's body on the cord, preventing a stillbirth. A long umbilical cord is just one possible cause of a prolapsed cord. The other frequent causes of this problem are a breech position, excess amniotic fluid and vaginal delivery of twins.