I'm 41 and I had an ultrasound done at 12 weeks (currently 14 weeks) and an initial blood draw called first look. The ultrasound fell within normal range (0.

. The second blood draw will be next week. The genetics counselor explained to us that even though we may have an abnormal first read, there is still a margin of error of about 15% or so. The second draw along with the first draw will be more definitive. However, she was pleased and told us we should be as well that the Nuchal translucency fell well within normal - as yours did. She also explained that these tests have a margin of error because the damaged chromosomes may or may not have divided to form the baby. In some cases a false positive means that the damaged chromosomes divided to form the placenta (which does not affect the baby). A false negative is the reverse, where the damaged chromosomes split to form the baby but the placenta cells are fine. The test measures or tests these cells. Lastly, she told us that it is the COMBINED blood work (since the second draw is a better marker, but still with a smaller margin of error) along with the ultrasound that is taken into account to come up with a statistical probability of whether we are high risk for chromosomal defects. This will in turn help us make the decision whether we will do an amnio later on. An amnio is accurate because it tests the fetal cells and not the placenta cells like the test your wife and I are having done at the moment.
I hope this helps answer your question. However, you may want to talk to a genetics counselor for a more informed answer and options for testing.
Congratulations on your pregnancy!