Definition

Thickening ³ 6 mm in the posterior aspect of the neck.

Explanation

This should not be confused with nuchal translucency which is a distinct measurement taken at 10-14 weeks. Neither should it be confused with a cystic hygroma, which is a septated, fluid filled structure around the fetal neck.

A thickened nuchal pad may be an early sign of hydrops but is usually an incidental finding.

Standard image for identification/exclusion

Transverse view of the cranium across the thalami, angled slightly posteriorly to include the cerebellum and occipital bone.

Technique for measurement/assessment

The nuchal pad should be measured by placing one cursor at the outer edge of the occipital bone and the other at the skin surface.

The ultrasound assessment should be completed, looking in particular for the other soft markers: echogenic bowel, echogenic foci, short femur length, renal pyelectasis and choroid plexus cysts. Signs of hydrops should also be sought.

Implications of a positive finding in isolation

The recent meta-analysis by Smith-Bindman et al suggests that the positive likelihood ratio for nuchal pad is 17 times the background risk for trisomy 21. This will result in the vast majority of people with this finding being considered high risk and justifies a discussion of karyotyping.
The consensus view at this time is for karyotyping to be discussed and offered, but we are aware of the deficiencies in the current evidence. Audit findings from the West Midlands data during 2000-05 support offering karyotyping for isolated nuchal pad.

Image 1 - Nuchal Pad

References

1. Nyberg DA, Luthy DA, Resta RG, Nyberg BC and Williams MA. Age-adjusted ultrasound risk assessment for fetal Down’s syndrome during the second trimester: description of the method and analysis of 142 cases. Ultrasound Obstet Gynecol 1998; 12 (1): 8-15, Abstract