"9 Surprising Facts About The Umbilical Cord"
This is a very interesing article and a reason I know my husband is worried about home birth without a midwife. But it's extremely rare that a short umbilical chord, or a baby being choked by it's lifesource (umbilical cord) happens.
Knots have been known to be in umbilical cords but "usually" nothing bad happens and oxygen and blood can still get through. It is rare when something like Amy's situation happens.