My parents fostered while I was growing up. Most of the infants/toddlers we had (around 12 over 6 years, including my DB who we adopted), came from alcoholic/drug addicted mothers.
We're talking litre of vodka or more a day + cigarettes + drugs.
Not a single child showed the physical symptoms of FAS, although 4 were ADHD/Asbergers/Autism (this was the 90's so the spectrum wasn't as defined). One (my DB who we adopted at 2) has gone on to abuse substances as well.
Certainly there were issues with all the kids, but that can be attributed to the fact that they were all victims of abuse as well as the general mental health issues stemming from their family backgrounds.
So, remembering the struggles of all these kids that I saw growing up, when I became pregnant I chose to have the occasional drink. I figured with my family background, the fact that I was eating properly, not smoking, not taking other drugs, a glass or two of wine every couple of weeks or a pint of beer, wasn't going to harm my child. They are 6 & 4 and fine. Bit of an issue with a lisp with DD, but that does run in our family, so not a surprise.
I think its really up to every woman to make their own decisions in this, with sufficient knowledge of the actual risks, rather than blanket statements that "no amount is safe", which is more about covering the NHS & insurance companies arses than it is about fetal or maternal wellbeing.