It is usually pretty easy to slip it over the head and deliver the rest of the baby. In some cases, it is so tight that it must be clamped and cut before birth. If this is the case, it is very important to deliver the baby without delay. In all the births I've attended, I've only had to clamp and cut before birth in two cases. If the baby is born and there appears to be no problem, generally there are no health risks.
Providers can observe certain fetal heart rate decelerations which indicate cord problems.
Delivery may be hastened or a cesarean may be done if the pattern looks ominous or is occurring over too long a time. When the cord compression is severe or long standing, the baby may have low Apgars and suffer brain damage, which could result in a degree of mental retardation or cerebral palsy. If the compression is severe enough and labor has not yet begun, the baby can die in utero and be stillborn. But again, this is a very common condition and most babies do just fine. Thanks for writing.