I wouldn't drink knowingly during pregnancy because I saw the effects of FAS with a family member whose mother drank. That being said, I did have a few drinks before I knew I was pregnant with my second son (he was a surprise) and I really worried perhaps I had unknowingly done damage having those couple of glasses of wine on two different nights, but he turned out beautiful and healthy.
It's just SO hard to say, some babies turn out fine and other babies end up with FAS when the mom drinks during pregnancy. It's just not worth the risk in my eyes. I beat myself up for months over those few glasses of wine and I guess that wasn't necessary either, but it's just a risk that is so easy to avoid.