Hi arabica, my dd had CPCs, echogenic something at her 13 week scan and she was small-for-dates. Doctor murmured something about Trisomy 18. Had a scan booked in the next day with Harris Birthright, Kings College Hospital, which confirmed the results. Had a CVS done on the same day, which eliminated the major chromosomal defects. But I had never been more frightened and out of control those few days and waiting for the results than I had even been.
I was offered regular scans thereafter. At 16 weeks and thereafter, dd's scan showed heart defects, short femur (she was always small-for-dates anyway), single umbilical cord. Were it not for the clear CVS, I would have doctors jumping on me from on high with doomsday scenarios. In the end, dd only had a big hole-in-her-heart. But the worry and stress of the scans ...
Most garden variety sonographers are not very well trained IMO. If you can somehow manage, don't panic. Just go for the fetal medicine dept scan - where they should know what they are seeing and can give you something more definitive.
Remember, scans pick up a lot of dodgy "soft markers" which in the majority of cases are actually perfectly fine. Do you have a stance on an amnio? I found that I was just expected to go for my CVS, just as wools was pressured into an amnio. In hindsight, it was the right thing and saved a lot of future worry, but I did not make an informed decision at the time.