I thought scholarship had been moving in the opposite direction, but here's a new argument for the view that Isaiah really did mean to say a virgin would conceive and not just a young woman. This seems to me to be a good argument. I was beginning to think the better arguments were for the more dominant view for a while, but I'm not so sure now.
I don't believe Isaiah 7 has to have an immediate reference to Mary's virginal conception to have some reference to it anyway, so nothing about the doctrine of the virgin birth is threatened by any conclusion here. The only issue is whether it allows an apologetical argument for Christianity based on a kind of fulfilled prophecy that couldn't be fulfilled any other way. I hasve two hesitations about seeing this as grounds for such an argument. First, it doesn't prove that Isaiah intended it to be about a virgin birth. After all, virgins do conceive on their first time having sexual intercourse. The grammar allows that even if the term requires a virgin. Second, there's no easy argument against those who would suspect Matthew, the only NT author to refer to the virgin birth, of doctoring the evidence to fit the prediction. Only one NT author refers to it. He's someone often described as misinterpreting prophecies, though I've argued against that. He also is seen by many as fitting Jesus' life to the way he read prophecy, moreso than other authors. The link I just gave has some response to that, but these people are conspiracy theorists, and it's very hard to refute a conspiracy theorist who sees everything as confirming their theory even if a perfectly plausible account fits the data when you don't share their assumptions. So for all those reasons I'm not sure this is one of the best apologetical arguments you can make. It might be helpful for some contexts, but there are too many moves someone can make to avoid seeing this as support for Christianity for me to see it as worth making very often.