A loop of umbilical cord around the fetal neck (nuchal cord) is a common finding at delivery. Nuchal cords have been associated with an increased risk for adverse outcome [1-3]. Whether prenatal ultrasound examination should attempt to identify the presence of nuchal cords and whether identification of affected pregnancies should alter antepartum and intrapartum care are controversial.
The term nuchal cord describes an umbilical cord that passes 360 degrees around the fetal neck. Nuchal cords can be classified as :
- Type A — A nuchal loop 360 degrees around the fetal neck where the placental end crosses over the umbilical end, entangling the neck in an unlocked pattern that can undo itself.
- Type B — A nuchal loop 360 degrees around the fetal neck where the placental end crosses under the umbilical end, entangling the neck in a locked pattern that cannot undo itself. This pattern can form a true knot when it passes down over the fetal body.
Nuchal cords can occur as single or multiple entanglements around the fetal neck. They may be loose or mildly to severely constricting. Disruption of the smooth contour of the fetal neck compressing the skin in that area, referred to as the "divot sign" , has been used to define tight nuchal cords .
The formation of nuchal cords may be a random event and/or related to excessive fetal movement or a long umbilical cord .