E.P.
I can't give you any specifics (its been a long time since I was pregnant). I can tell you, however, that labs can sometimes give a false positive and/or not mean anything. My friend had a false positive early in her pregnancy and spent the next several months worrying herself sick. She was told the baby most likely had downs syndrome (not terrible of course, just not what you might want to hear). The doctor she met with tried to bully her into getting an amnio and she refused (she didn't like the risk statistics). After a few months, she was able to get a detailed sonogram (3d?) and everything was 100% fine. She couldn't help but think what might had happened if she had the amnio and lost the baby (I also know someone that happened to where the baby was 100% fine and healthy - although this is VERY rare, it can happen).
So - please don't worry - it's most likely nothing to worry about. I'm going to pray for you and your family.