Nuchal cord on ultrasound: how to identify it, what it means and how to report it without alarm

A nuchal cord is a 360-degree loop of umbilical cord around the fetal neck, present in 22% of births in the Hayes (2020) meta-analysis, and most are not associated with perinatal morbidity or mortality. Because the finding is common and of limited predictive value, the report should describe it objectively, without turning a frequent variation into a cause for alarm.

How to identify a nuchal cord

• Assess the neck region in sagittal and transverse views, with color Doppler on a scale suited to slow flow.
• Confirm that the cord encircles the neck. A cord merely lying against it, without completing the loop, is not a complete nuchal cord.
• Count the loops when they can be separated.
• Divot sign: an impression of the cord on the skin at the back of the neck, visible on gray-scale in the sagittal plane. Do not confuse it with posterior cystic masses, skin folds or fluid pockets.

Performance of the scan

• Jauniaux 1992: color Doppler sensitivity of 79% versus 33% for gray-scale, higher after 36 weeks (93% versus 67%, according to the Peesay review), and better for multiple loops (94%) than for a single loop (72%).
• Peregrine 2005: in 289 women before induction, sensitivity 37.5%, specificity 80%, positive predictive value 29% and negative predictive value 85%.
• Smaller, more recent studies report Doppler sensitivity above 90%. The figures diverge widely, so a negative scan does not exclude a nuchal cord at delivery.
• The finding also changes over time: free-sliding loops can undo themselves. Frequency rises with gestational age, from about 6% at 20 weeks to 29% at 42 weeks.

Clinical significance

• Hayes 2020 found no association between nuchal cord and stillbirth (OR 1.11; 95% CI 0.62 to 1.98). For multiple loops the estimate was 2.36 (95% CI 0.99 to 5.62), not statistically significant. The authors could not analyze tight or loose loops.
• A true knot is a different finding: it was associated with stillbirth (OR 4.65; 95% CI 2.09 to 10.37).
• Multiple loops occurred in 4% of births.
• Peregrine 2005 saw no increase in cesarean or poorer neonatal outcome, and a study of uncomplicated post-term pregnancies concluded that looking for it before induction was neither necessary nor useful.
• The Peesay review notes that a nuchal cord can relate to variable decelerations and that tight loops can, in rare cases, have neonatal effects. The subject remains controversial.

How to report without alarm

Describe what was seen in neutral terms, for example: "Complete nuchal cord present, with one loop." Alongside it, record what actually informs fetal well-being: movements, amniotic fluid, cord of usual appearance and, when performed, Doppler. Avoid words such as "strangled" and "wrapped tight", and do not link the finding to a risk of fetal distress or to mode of delivery: management belongs to the obstetrician, considering the case as a whole.

What the report should include

• Presence or absence, if the service chooses to mention it.
• Type: complete or incomplete, and number of loops when it can be determined.
• Impression on the cervical subcutaneous tissue, if any.
• Cord vessels and other findings, such as a suspected true knot.
• Well-being data from the scan.

Common mistakes

• Reporting a nuchal cord without color Doppler.
• Calling a cord that is merely near the neck a nuchal cord.
• Stating "no nuchal cord" as a guarantee for delivery.
• Adding risk statements to the conclusion without support in the findings.
• Confusing the divot sign with a skin fold.

See also our articles on the third-trimester report, obstetric Doppler and the fetal biophysical profile.

How Laudário helps

In the Umbilical Cord tab of the second and third trimester obstetric template of Laudário:

• The nuchal cord has the options do not mention, absent, incomplete and complete, with the number of loops.
• Impression on the cervical subcutaneous tissue and true knot have their own fields.
• The text comes out as a neutral, standardized sentence, including in the conclusion.

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References

• Hayes DJL, Warland J, Parast MM, et al. Umbilical cord characteristics and their association with adverse pregnancy outcomes: a systematic review and meta-analysis. PLoS One 2020;15:e0239630.
• Peesay M. Nuchal cord and its implications. Matern Health Neonatol Perinatol 2017;3:28.
• Jauniaux E, Mawissa C, Peellaerts C, Rodesch F. Nuchal cord in normal third-trimester pregnancy: a color Doppler imaging study. Ultrasound Obstet Gynecol 1992;2:417.
• Peregrine E, O'Brien P, Jauniaux E. Ultrasound detection of nuchal cord prior to labor induction and the risk of Cesarean section. Ultrasound Obstet Gynecol 2005;25:160-164.