My birth control failed after I'd already had a child with severe impairments. The child I carried had a 65% chance of being born with the same problem. I didn't abort. Having more kids than we could handle led directly to our divorce. I love my child, but I would have been better off aborting.
It's legal and available. If you think it's your best choice, you should do it. If you know you can't do this on your own, be honest with yourself. Many people try to make abortion a huge moral issue, but having a child you can't cope with is the true moral issue. Use better birth control after, like Depo-Provera shots, or something permanent if possible.
Email me if you want to talk. My thoughts are with you.