T., I had this same issue with my OB when I was pregnant with my first daughter (I was 24). They had me all worked up and worried, sent me to the high risk OB, had more ultrasounds, and then tell me there's a 33% chance baby has major genetic defect, 33% chance its a major heart or lung defect, or 33% chance her lymphatic system is immature and everything is perfectly fine. At this point we opted for the amnio because my sanity needed relief. As it turns out, she was perfectly fine, and we had a very healthy little girl. For my second pregnancy, I switched OB's and when he saw in my chart that they had even checked nuchal thickness on a 20-something mom, he was upset. He told me that test is only for mothers in the mid-late 30's who are at higher risk. We never checked it on my second daughter, and for me, that was a relief! After going through all of that, I wouldn't want to know (that's just me). My second pregnancy was much more relaxing.
My advice is that if you need more info to make yourself feel better, then do it. BUT don't cause any extra stress on yourself by worrying over it because since my situation, I have heard of many more women who had the same issue and the baby was completely fine. Relax, enjoy your pregnancy, and have hope and pray for your perfectly beautiful new little angel.