nuchal cord
description
a single, double, or triple loop of umbilical cord around the neck occurs in 20%, 2.5% and 0.5% of deliveries, respectively. as many as nine nuchal coils have been observed. the frequency of a nuchal cord increases with advancing gestational age. a nuchal cord is present in 5.8%, 22.0% and 29.0% of deliveries at 20,30 and 42 weeks’ gestation, respectively. fetal death from strangulation is therefore, a rare event. in fact, larson and co-workers have reported that the rate of fetal death in utero occurred less frequently with a nuchal cord than in its absence (0.6% vs 1.2%, p = 0.07).
diagnosis
there are two patterns of nuchal cord. in type a, the placental end of the umbilical cord crosses over the umbilical end. since the umbilical end of the cord is longer and usually not taut, this pattern may become undone by fetal movement. however, if the placental end crosses under the umbilical end (type b), the nuchal cord will not loosen or become undone. the potential for fetal morbidity and mortality appears to be increased with this latter pattern.
differential diagnosis
frequently the umbilical cord may fall around the neck for 180 to 270 degrees – this is not a nuchal cord. color doppler is helpful in confirming that the umbilical cord extends all the way around the neck. occasionally, a nuchal cord must be differentiated from multiple loops of intra-amniotic bowel associated with gastroschisis. color doppler will differentiate between these two possible diagnoses.
sonographic features
if the loop or loops of umbilical cord are sufficiently tight to make an impression on the nuchal skin, the sonologist/sonographer should be concerned about the potential for an in-utero fetal demise.
the initiation of a heart rate deceleration or acceleration with manual compression of the area over the fetal neck is further evidence of a nuchal cord.