Ultrasound Results - Chromosome Error - What does it mean?

We had an ultrasound at 20 weeks on Monday, and got our results on Friday.  The doctor told us that they had found a small mass by the umbilical cord, which could mean a chromosome error or that the intestines are growing on the outside of the stomach.  I realize that it is possible they are mistaken, but in the case of a chromosome error, what exactly does that mean?  Is it possible that this pregnancy will end in the future because things are going together right?  She told me what would happen if it was the intestines, its the chromosome results I don't understand.  Has anyone experienced this / know what it could potentially mean?  We have a level 2 ultrasound on Thursday, but I'd like to know ahead of time what we might have ahead of us.  Thanks in advance...

[peekawho]

There are some types of chromosomal abnormalities that are associated with certain ultrasound findings, or "markers".  Perhaps what they believe they have seen around the umbilicus is associated with a particular chromosomal abnormality.  By no means however, does it mean that every baby with a certain ultrasound finding will have a chromosome abnormality.  

Good luck, and keep us posted.