Ted,
Since you and your wife have already been identified as carriers an amnio should give you a very simple yes or no. A child must have 2 CF mutations (one from mom, one from dad) to have CF, and only one CF mutation to be a carrier. There are pro's and con's to an amnio, risks and such. I trust those things have already been discussed with your doctor. There are a few on this site who were diagnosed via amnio when their carrier status and mutations were known. It is a simple match up of your mutations to the sample taken from the amnio.
Things you have to think about and discuss amongst yourselves though: will we terminate the pregnancy if + for CF? If we are + for CF what are we going to do about it? (mental preparation, saving some $$$, ensure adequate insurance coverage). If + for CF, what steps will your doctor/delivery hospital do to ensure a safe delivery-is your hospital even equipped to handle a ruptured bowel, abnormal sized bowel.... if that occurs? If not, will you make a plan B, C...? If it were me, personally I would do it just so I could get prepared. but to each his own, and no judgement for whatever you choose to do and whatever you choose to do based on the results.
As far as a correlation between the NT and CF, I have not heard of this. It is possible someone else might have some more information regarding this though.
I have a question though about the sweat test on your son. Did your doctor give any indication as to why in the world they choose the sweat test (other than it being the cheapest method), or is that the method you requested? I have to scratch my head at this one (if it's the doc's choice) because
1. Sweat tests are known to give false negatives, repeatedly. Many test positive only after a blood test identifies 2 CF mutations.
2. Depending on the age of your son, infants and some very young children don't respond well to the sweat tests (not enough sweat, wouldn't sit still long enough for truely accurate results...)
3. If you two have already been identified as carriers your mutations are known. Why not have a blood test done on your son? That will give you a difinitive YES or NO and will even let you know if he IS or IS NOT a carrier so years down the road when he's starting his own family, he's aware of the situation. I know you didn't ask for any recommendation regarding this, so I hope I don't offend you, but if your son's results come back borderline or if he exhibits anything that resembles a CF symptom I would highly recommend the blood test. They already have you to match it to so it should be a VERY simple test.
Hope this helps a bit, please let us know if you have anymore questions, were here to help!
