The AFP test looks at a number of different possibly birth defects/syndromes---Did the doctor specifically tell her it indicatd an increased risk for Down's Syndrome?
I have also NEVER heard of anyone being told after a sonogram that their was decreased brain activity. I am not aware of a sonagram that does that-- though maybe there is something new out there. (I know with my kids they could show me blood flow to the brain etc)
There are 'markers' that can be seen on a Level III if present pretty much confirm the Downs-- but the only definititve way to say 'no' to the presence of Down's is to have amnio. (which has risks and requires yet another sono. --I had a heck of a time getting my insurance to pay for the additional sono! I kept saying "YOu want my doc to do the amnio w/out it????")
Was she pushed by the doc. to have the AFP test? I had an 'elevated risk' of down's with my first and refused this test with my other kids. (By my third I was refusing all of the tests and treatments...) I told my doc that I wouldn't be terminating my preg. so I didn't see the need to have the additional stress and/or health risk (b/c of my age it would have been likely that AFP would be 'off' and I would end up with amnio. recommended. After my sono. with #2 baby I had to fight with the high risk ob to NOT have amnio and he treated me really poorly.)
Please assure her that w/ the AFP test there are WAY more false positives than anything else. That is why it is a 'SCREENING' tool and not 'DIAGNOSTIC'. I know that age will affect the result..if preg dates are off that will affect it. I suspect that having a child with Down's in the family tree might also flag them to elevate the risk.
If she does have additional testing and finds out that her child does have some disability- she can use the remainder of her pregnancy to prepare. And if it is Down's ---there is so much variability in their abilities and so much more that can be done to maximize their abilities.