My ob said that I had nothing to worry about because it was his grandmother who had the kids and if it was a brother or sister I should be concerned but my doctor said I should deff have one done so after the nt, if anything looks suspicious obviously I'm having whatever is nessasary done to make sure everything is okay or known before we have this baby. Everyone in his family is telling me I need to have it done incase it does skip generations or something. I'm not even sure if they are doing a blood test with the nt scan or not. She didn't say they were and didn't say they weren't but from hat I've heard it's rare for them to do one without the blood test.