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Nuchal Cord

Umbilical Cord (arrows) encircling the posterior neck
Color Doppler imaging of the nuchal cord

Findings:

The umbilical cord (arrow) is seen posterior to and encircling the nuchal area.

Discussion:

Virtually every sonologist will at least once in their career be confronted with the sonographic finding of a nuchal cord. In many respects this finding is analogous to subtle isolated findings reported to be associated with chromosomal abnormalities. The major issue is what to do with the finding: report it, disregard it or alter obstetrical management. While there is certainly no consensus as to how to 'deal with' this issue, there are numerous articles discussing the subject. Recently an excellent review and editorial on the subject of nuchal cords appeared in the journal Ultrasound in Obstetrics and Gynecology by Drs'. Sherer and Manning. This is an excellent review of the subject and the reader is encouraged to read this in detail. What follows is a summary of the salient points raised in this review as well as other published reviews of the subject.

The reported prevalence of nuchal cords (entanglement around the fetal neck) has been reported to be between 8%-30%.The incidence of single, double, triple or quadruple nuchal cords at delivery have been reported to be 10.6%, 2.5%, 0.5% and 0.1% respectively, by Shui et al. The prevalence of nuchal cords increase with advancing gestational age. In a report by Larson et al, they found that the incidence of nuchal cords increased from 5.8% at 20 weeks to 29% at 42 weeks gestation. The increase is thought to be due to either increased fetal activity and or decreased amniotic fluid volume. It should be remembered that nuchal cords have also been reported to reduce spontaneously during gestation. The etiology of nuchal cords is controversial and unclear. Strong et al have demonstrated that fetuses with nuchal cords have less vascular coiling than those that do not (65%). The theory being that less coiled cords are more flaccid and more susceptible to nuchal entanglement. Some researchers have found that male infants have longer umbilical cords and that the occurrence of nuchal cords is associated with increasing lengths of the cord. This has not been confirmed by other investigators.

Perhaps the most important and controversial issue raised with nuchal cords is whether there is an adverse effect on perinatal and neonatal outcome. There are numerous reports demonstrating an association of nuchal cords with: meconium stained amniotic fluid, abnormal fetal heart rate pattern, operative vaginal delivery, low 1-minute Apgar scores and mild umbilical acidosis at birth. Two studies by Larson et al however concluded that despite these associations there was no added risk of adverse neonatal outcome and that the risk of an antepartum stillbirth was not increased in the presence of a nuchal cord entanglement. Recently, Nelson and Grerher evaluated the association of cerebral palsy with conditions that can interrupt oxygen supply to the fetus as a primary pathogenic event. These authors performed a population-based case-control study comparing birth records of 46 children with disabling spastic cerebral palsy without recognized brain lesions and 378 randomly selected controls. Eight of 46 children with otherwise unexplained spastic cerebral palsy (all eight exhibited quadriplegic cerebral palsy) and 15 of 378 controls had births complicated by 'tight nuchal cord' (odds ratio for quadriplegia, 18; 95% confidence interval, 6.2-48). Nelson and Grether concluded that potentially asphyxiating conditions, chiefly tight nuchal cord, were associated with an appreciable proportion of unexplained spastic quadriplegia but not with diplegia or hemiplegia. Nelson and Grether later calculated that, if they were correct (that indeed a tight nuchal cord played a significant role in the cerebral palsy of only eight children from among 155 636 who survived to 3 years of age), approximately 20 000 pregnancies would need to be imaged to identify a single instance of a tight nuchal cord that would be later followed by cerebral palsy. Furthermore, these authors state that, because the frequency of tight nuchal cord in utero is unknown and because it is not known whether a tight nuchal cord may spontaneously loosen, it is not clear that intervention would provide benefit. Another study by Clapp et al evaluated long term follow-up of nuchal cord on neurodevelopment in infants at one year of age. The authors concluded that nuchal cord at birth has significant association with subclinical defects in both mental and psychomotor performance at 1 year, especially in the presence of the above-mentioned complicating factors.

The number and type of nuchal cord entanglements have been reported to be associated with differing morbidity. Osak and et al reported that infants with nuchal cords at delivery were significantly smaller and had birth weight to placenta weight ratios significantly smaller than infants without nuchal cords. Furthermore, a 'dose relationship' was noted in that these effects were greater in infants with more than one umbilical cord encirclement. Lipirz and colleagues, however, were not able to demonstrate an association between a nuchal cord coiled twice or more around the neck (8.3% of cases) and decreased birth weight. Collins reported a 'significant incidence' of stillbirth associated with the umbilical cord wrapped around the head in a 'locked fashion' which has been addressed as nuchal cord type B. The designation of type A or type B patterns of nuchal cord depends on whether the umbilical end crosses over (type A) or under the placental end of the umbilical cord (type B). Among 850 deliveries of low-risk pregnancies, three cases of nuchal cord type B were noted. Two fetuses were delivered by Cesarean section due to fetal distress and one was stillborn at 32 weeks' gestation with a nuchal cord times three (one of which was type B). It is, however, unclear in this case, as in other reports, whether the umbilical cord entanglement was the direct cause of pregnancy loss or an unassociated, incidental finding.

As one would imagine, sonography is uniquely capable of making the diagnosis of nuchal cord entanglement. Accurate diagnosis requires that both sagittal and transverse sections are obtained to avoid a false positive diagnosis of this condition. Many cases may demonstrate an umbilical cord adjacent to (yet not encircling) the fetal neck. Indentations of the posterior neck by the nuchal cord has been referred to as the 'divot sign'. This appearance may be due to normal folds of skin or posterior neck masses. In cases in which the diagnosis is uncertain, color Doppler imaging or Doppler flow velocimetry may assist in confirming the diagnosis. Abnormal Doppler velocimetry mainly consists of abnormal systolic to diastolic ratios and early diastolic notching Likewise, three-dimensional ultrasound may also improve diagnosis of nuchal cords.

Color Doppler image demonstrating nuchal cord encircling the neck (arrow)

Same case as on the left. The umbilical cord extends and crosses anteriorly

After an extensive review of the subject Sherer and Manning made the following observations: "Given the lack of solid evidence of significantly increased incidence of adverse neonatal outcome with a single (or even multiple) nuchal cords and the case report nature of perinatal mortality associated with nuchal cord involvement, upfront, one could argue against any implications as to any involvement whatsoever in the non-compromised fetus. However, it is our strong belief that, due to the potential (although usually rare) associated less-than-optimal outcome, and in concert with current medical ethics, this information should not be withheld and accordingly should he forwarded to both the patient and her attending physician. This preferably would be in real time during the examination and explicitly on the written report generated following the encounter. In such cases, the patient should be guided as to the critical importance of monitoring fetal movements and be instructed to contact her physician with any change in fetal movement patterns. When further complicating issues are confronted, such as significantly decreased amniotic fluid volume, postdates, fetal growth restriction, and especially decreased fetal movements, immediate and repeated fetal testing measures should be sought. With less than optimal fetal testing, delivery should be considered."

 

References:

Sherer DM, Manning FA. Prenatal ultrasonographic diagnosis of nuchal cord (s): disregard, inform, monitor or intervene? Ultrasound Obstet Gynecol 14:1-8, 1999

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Larson JD, Rayburn WE, Harlan VL. Nuchal cord entanglements and gestational age. Am J Perinatol 14:555-7, 1997

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Peter W. Callen, M.D.
Professor of Radiology, Obstetrics, Gynecology and Reproductive Science
University of California Medical Center, San Francisco, California