Mum keeps telling me to have an abortion!

I'm almost 26, I have a 5 year old daughter and I'm currently 15 weeks pregnant. My relationship and recently broken down and soon I'll be living by myself. Although we aren't together me and my ex are still friends and he has promise to stand by me and support me. It's not the baby's fault that this has happened and I can't imagine having an abortion. :( I just don't know why my mother keeps telling me this. Any advice please?