S.,
I think there are some important things that you should consider when making this choice:
1) YOU and only you can make the choice (with your husband, of course). Others have said what *they* would do or did do, but they are not you.
2) No two situations are identical ... that includes the severity of the defects involved with any diagnosis, including Downs. It's not all like what you see on TV. You need facts to make an informed decision. Please consider meeting with a genetic counselor who can give you facts and help you sort through the information you receive. You can do this now, prior to making the decision about amnio.
3) Cystic Fibrosis can be ruled out with a simple blood test on you. But the ONLY way to know about chromosomal defects, like Downs, is to have the amnio. Well, CVS, too, but you are too late in the pg for this test. The quadruple screen and future ultrasounds are screening tests only - when it comes to chromosomal defects. They will give you a 1 in X number liklihood of a defect occuring, but only amnio can give you a yes or a no.
4) There is a risk with any invasive testing, like amnio. Talk to your doctors about who would be performing the test. Would they send you to specialists? Experience and expertise of the doctor are crucial in regards to safety of the procedure. If you choose to have the test, reduce your risk as much as possible by choosing the best-qualified doctor to perform it.
5) Even if you already know for certain that you would not consider terminating the pregnancy regardless of the diagnosis, there are advantages to having as much information as possible prior to delivery. There are situations where a child would need to be delivered via C-section in order to survive. And there are cases where a baby might need emergency surgery at birth or other special considerations. Knowing these things prior to delivery would help the doctors take the best possible care of you and your baby. The decision about whether or not to have amnio is not all about asking yourself if you would terminate or not based on the results. There are other important things that can be gained by knowing versus not knowing.
Please ask your doctors about referring you to a genetic counselor as soon as possible. They could really be a help to you as you consider your next step.
All the best to you and your family.