During delivery, the umbilical cord sometimes gets wrapped around the baby’s neck. This is known as a nuchal cord. Occasionally, the cord can be wrapped around the neck two, three, or more times. For women and their obstetricians, this has historically been a condition of concern. In fact, Hippocrates called a nuchal cord “one of the dangers of eight month.” But is there really any danger to nuchal cords?
A Common Condition
Nuchal cords are common. Any type of nuchal cord is seen in 23-33% of all pregnancies. Single cords are the most common, occurring in 23-34%. Double cords are found in 2.5-5% of pregnancies, and triple cords in 0.2-0.5%. There are isolated cases of cords wrapped around the neck more than three times, with nine being the highest number of loops reported.
Nuchal cords are not usually seen on ultrasound before 20 weeks gestation because the cord is shorter than the fetal body until that time. But due to the movement in the womb, even a triple cord seen at 20 weeks can resolve by the time of delivery.
One study of 367 pregnancies in 2005 found an average cord length of 50-58 cm (19.7-22.8 inches). Researchers noted that longer cords tended to become looped around the neck, although nuchal cords did occur with shorter cords, as well. However, shorter cords were found to be more tightly wrapped around the neck.
Possible Dangers of a Nuchal Cord
The umbilical cord contains two arteries and a vein that carry blood between the placenta and the fetus. For centuries, nuchal cords were thought to be a problem during delivery. When the cord becomes compressed or overstretched during delivery, blood flow to the fetus is compromised, leading to a slow heart rate or bradycardia (less than 100) in the fetus. This slowing of the heart rate is also known as “variable heart rate decelerations.”
This is usually not dangerous, as it is temporary. As long as the heart rate returns to normal (120-160 for the baby), then nothing bad happens to the mother or baby. But if the heart rate remains low, then the medical team will act to relieve the cord compression that is presumed to be causing the bradycardia. Such measures include giving the mother oxygen or fluid, having her change position, slowing down her contractions with medicine, or, in extreme cases, performing a cesarean section.
Are Nuchal Cords Really harmful?
Historically, nuchal cords were thought to cause all kinds of negative outcomes at birth. However, multiple studies over the years have refuted this. One study in 2006 analyzed 512 deliveries but found that irregularities in fetal heart rate were not increased in those with nuchal cord. The only outcome that differed between babies with and without nuchal cord was a lower Apgar score (<7) at one minute in the nuchal cord group. But the Apgar scores at five minutes were not different, and there was no difference in admission to the neonatal intensive care unit.
A similar study on 350 deliveries showed that there were some differences in birth outcome between babies with loose nuchal cords (the cord could easily be uncoiled before delivery) and tight nuchal cords (the cord had to be clamped and cut before delivery). Compared to a control group without nuchal cord, the group with the tight nuchal cord was more likely to experience fetal distress during delivery and to have a low Apgar score (<7) at one minute. The loose nuchal cord group did not differ from the control group in these outcomes.
Another study comparing 218 pregnancies with nuchal cords to 190 pregnancies without nuchal cords found no differences in one and five minute Apgar scores or in the cord blood pH values (low pH in cord blood is a sign of fetal distress) between the two groups.
And in one of the largest studies on nuchal cords, investigators reviewed 4404 pregnancies and found that only nuchal cords of three turns or more were associated with a higher incidence of meconium-stained fluid, admission to the neonatal intensive care unit, fetal distress, and emergency cesarean section. However, the Apgar scores in these babies were not any different, which suggests that even nuchal cords of three or more turns don’t affect ultimate neonatal outcomes.
So the truth is, nuchal cords never really cause severe problems in the newborn, but are a source of concern for the mother and the obstetrician. Minor problems may arise only in cases with very tight nuchal cords or cases with three or more turns, but even these cases are manageable and don’t lead to serious consequences. If your baby is noted to have a nuchal cord on ultrasound, it may resolve by the time of delivery. And if not, a vaginal delivery is still possible and safe.