Current Perspectives of Prenatal Sonographic Diagnosis and Clinical Management Challenges of Nuchal Cord(s)

Abstract

Umbilical cord accidents preceding labor are uncommon. In contrast, nuchal cords are a very common finding at delivery, with reported incidences of a single nuchal cord of approximately between 20% and 35% of all singleton deliveries at term. Multiple loops occur less frequently, with reported incidence rates inverse to the number of nuchal cords involved. Rare cases of up to 10 loops of nuchal cord have been reported. While true knots of the umbilical cord have been associated with a 4–10-fold increased risk of stillbirth, nuchal cord(s) are most often noted at delivery of non-hypoxic non-acidotic newborns, without any evidence of subsequent adverse neonatal outcome. Prior to ultrasound, nuchal cords were suspected clinically following subtle (spontaneous or evoked) electronic fetal heart rate changes. Prenatal sonographic diagnosis, initially limited to real-time gray-scale ultrasound, currently entails additional sonographic modalities, including color Doppler, power Doppler, and three-dimensional sonography, which have enabled increasingly more accurate prenatal sonographic diagnoses of nuchal cord(s). In contrast to true knots of the umbilical cord (which are often missed at sonography, reflecting the inability to visualize the entire umbilical cord, and hence are often incidental findings at delivery), nuchal cord(s), reflecting their well-defined and sonographically accessible anatomical location (the fetal neck), lend themselves with relative ease to prenatal sonographic diagnosis, with increasingly high sensitivity and specificity rates. While current literature supports that single (and possibly double) nuchal cords are not associated with increased adverse perinatal outcome, emerging literature suggests that cases of ≥3 loops of nuchal cords or in the presence of a coexisting true knot of the umbilicus may be associated with an increased risk of stillbirth or compromised neonatal status at delivery. This commentary will address current perspectives of prenatal sonographic diagnosis and clinical management challenges associated with nuchal cord(s) in singleton pregnancies.

Keywords:

• prenatal ultrasound
• nuchal cord

Summary

Prenatal sonographic diagnosis of nuchal cord(s) is currently readily available with real-time, color, and power Doppler, and three-dimensional technology. Nuchal cord(s) represent a dynamic condition in utero, and may form or alternatively undergo spontaneous resolution at times within days, if not hours. Therefore, 100% prenatal sensitivity and specificity values in prenatal sonographic diagnosis of nuchal cord(s) at delivery are neither expected nor attainable. Nevertheless, current (acceptable) sensitivity rates continue to increase.

Given the previously described abundant protective mechanisms of the extracorporeal component of the fetal cardiovascular system, the umbilical vessels are exceptionally protected from potential compressive and/or shearing forces. It is not surprising, therefore, that the vast majority of fetuses with nuchal cord(s) are not at increased risk of adverse perinatal outcome prior to or during labor. This notwithstanding, emerging data suggest that multiple loops of nuchal cord (≥3), especially in the presence of compounding factors, mainly consisting of compromised inherent protective mechanisms of the umbilical cord vasculature, or in the presence of a placental insufficiency-associated fetal growth restriction, or coexisting true knot of the umbilical cord, the risk for stillbirth or compromised neonatal status at delivery appears likely to be increased. Assuming that all labors are conducted with continuous electronic fetal monitoring, no clinical advantage has been proven regarding intrapartum depiction of nuchal cord(s), as any potential compromise of the umbilical cord will manifest primarily with fetal heart rate changes and, if warranted, actions will be taken secondary to these changes even in the absence of imaging depiction of the presence of nuchal cord(s). Thus, if any clinical advantages are to be attributed to prenatal diagnosis of nuchal cord(s), these would entail increased antepartum fetal surveillance to decrease potential stillbirth in selected cases. In our assessment, third-trimester prenatal sonographic diagnosis of nuchal cord(s) should be documented, reported, and discussed with the patient. Although there is currently a clear absence of prospective (randomized) data, we believe that prenatal sonographic diagnosis of multiple loops of nuchal cord (≥3) should lead to antepartum testing for fetal well-being. Potential confounding factors associated with an increased risk for adverse outcome should always be sought, and in their presence, increased fetal surveillance may be warranted even in the case of a single nuchal cord. Simply negating the potential clinical benefit of prenatal diagnosis of nuchal cord(s), given the usual uneventful outcomes associated with this condition at delivery, in our belief represents a likely unethical, scientifically incorrect oversimplification. Close prenatal fetal surveillance appears to be indicated in selected cases, and consideration should be given to delivery if and when indicated.

Disclosure

The authors report no conflicts of interest in this work.