Nuchal Edema

Subcutaneous accumulation of fluid considered an early sign of fetal hydrops (1).

Echogenic area between the skin surface and the occiput or spine, representing subcutaneous accumulation of fluid.
Seen between 14 and 18 weeks gestational age (at 18-20 weeks measurement of nuchal thickness becomes unreliable due to the wide range in the normal rate of development of the fetal neck muscles and subcutaneous tissue).
Echogenic area greater than 6mm.

Calipers placed from outer skull table to outer skin surface

Normal range = 1- <5 mm

Borderline range = 5 – 5.9 mm

Abnormal = 6 mm

Measurement can be overestimated by angling caudally, intersecting the inferior level of the cerebellum and occiput

Diverse causes including: trisomies, cardiovascular and pulmonary defects, skeletal dysplasia, congenital infection, metabolic and hematological disorders.
Karyotyping is recommended in all cases (2).
Nuchal edema + no other structural abnormalities (cardiac or non cardiac
Þ about one third of fetuses will have a karyotypic abnormality (usually Down Syndrome and less commonly Trisomy 18)
Þ about two thirds will have a normal karyotype.
Nuchal edema + cardiac and non-cardiac structural abnormality
Þ majority of fetuses will have chromosomal aneuploidy.
Nuchal thickening in Down syndrome may resolve prior to 16-18 weeks (3).

Nicolaides KH, Azar G, Snijders RJM, Gosden CM. Fetal Nuchal Oedema: Associated Malformations and Chromosomal Defects Fetal Diagn Ther 1992, 7:123-131
Suchet I. Ultrasonography of the fetal neck in the first and second trimesters. Part 2. Anomalies of the posterior nuchal region. Can Assoc Radiol J 1995; 46:344-352
Bromley B, Benacerraf BR. The resolving nuchal fold in second trimester fetuses: not necessarily reassuring. J Ultrasound Med 1995; 14:253-255
Comas C, Martinez JM, Ojuel J et.al. First trimester nuchal edema as a marker of aneuploidy. Ultrasound Obstet Gynecol 1995; 5:26-29

Diffuse nuchal edema