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There are two distinct patterns, illustrated by the images. A smooth elevation of thin skin with ultrasound shining through a simple fluid space (nuchal translucency, NT) and a "shaggy lion's mane" of multiple dilated lymphatics (NL). NL represents a tissue malformation and has a very high association with chromosome problems. NT involves a circulatory overload and has a lower association with chromosome problems and a higher association with other syndromes. A slight degree of NT is normal 6 weeks after conception and is typically gone during the next week of development. NT is identified when the elevated fluid rim is obvious and stage is after 10 weeks GA. NT can be transient in normal fetuses, at other times it progresses to congestive heart failure.
Neck findings are best sought between 10 and 14 weeks GA. Afterwards, there is sufficient lymphatic development that NT it not often found, even when there is aneuploidy. An amnio should always be done when there is a question or worry about aneuploidy, whether there are neck findings or not. Absence of NT or NL do not exclude chromosome problems.
