Thanks for your replies. And for those of you who didn't read my second message, the man in this situation is my friend, not the woman. I hardly know the woman, and wouldn't attempt to communicate with her about her decision.
I know this is their decision entirely, but I'm having to think very carefully about how I talk to him about it, since I'm the only person he has told. He's not sharing his thoughts, experiences or feelings with anyone else, not his family or other friends. So, I feel that the pressure is on me to really help him think this through properly.
But I feel very strongly that his reasons for asking her to have an abortion are extremely selfish. I agree that his having already requested this will have been very damaging to their relationship anyway, regardless of whether they keep the baby or not.
But I think he is completely, utterly deluded if he thinks he can coerce her into aborting a child she wants, and expect their relationship to continue from where it left off. He sees it as if he's pressing a 'stop' button. When I spoke to him yesterday and asked him how he'd imagine things to be after the abortion had happened, his answer was very vague and this didn't fill me with confidence that he really had a clue what he was doing.
I think the abortion will destroy their relationship. I think this may be the only chance he has at a decent relationship, and at having children (he is extremely shy and socially not very easy, so it has taken him this long to find a girlfriend... chances of him finding another one, let alone another one that wants to have kids is very slim, I think - pessimistic, I know, but I know him extremely well). I think he will end up back in his very lonely, boring life that he had prior to this relationship.
I feel that I ought to tell him at least some of these feelings I have, because I think he will bitterly regret this decision in the future, and I would regret not at least attempting to help him resolve some of his doubts before aborting his child.
Thanks for your replies!