After much consideration, I'm leaning towards "yes". That's no life for a child to have, and into their adult lives they would never develop. Fair enough, they wouldn't necessarily know they should be developed, but it's not really giving them a fantastic chance/standard of life.
And, for more selfish reasons, having a Down's Syndrome suffering child would be quite a burden, both on me and the father, and any friends and family who tried to help out when they could.
I'm not saying that people with Down's should be allowed to live or anything but, personally, I don't think it's fair on them if you know what will happen. I appreciate the fact that those people still have emotions and can think on their own level just...well, I've explained already.
On the other hand...aren't all humans entitled to the right to life? I dunno, I think this might be one of those questions you can't honestly answer until it happens to you.
I'm not at all anti-abortion, unless it's the mother's 5th or 6th one because she was too stupid to use protection, but...it's still a touch decision to undertake, and I really feel for those who have to make the choice, in any circumstance.