The incidence of true knots is 0,5% – 1%. Nuchal cord with one loop is found in 20% of deliveries, two or three loops in 2.5% and 0.5% respectively. Cord prolapse is estimated to occur in 0.4% of deliveries.

Blood flow is compromised if the knot or nuchal cord tightens. The tightening occurs most often during delivery. Decreased venous return from the placenta leads to asphyxia. Cord compression may cause neurologic damage, intrauterine or intrapartum death. Perinatal mortality is approximately 10% in the presence of prolapsed cord or true knot.

Strangulation by amniotic bands causes fetal demise.