Ultrasound at 12 weeks showed nuchal translucency was 4mm. what does this mean?

Nuchal Translucency : Nuchal Translucency is a screening test to determine risk of chromosome abnormalities in a fetus. When the NT is greater than 3.5 mm, there is a 1 in 5 chance of a chromosome abnormality such as Turner or Down syndrome, or Trisomy 18. Additional tests should be ordered by an OB or genetic counselor for confirmation. A mother may decide to continue or end of the pregnancy based on the information.