Opinions on terminating a pregnancy due to birth defect?

Hi. I'm 17 years old and pregnant with my first baby. First off I'd like to point out that even though I am only 17 I am far from a statistic. I graduated high school early and am taking night cles at my local community college as well as working a full eight-hour shift during the day. I'm not some irresponsible teen, I'm doing what I need to to make sure my baby had a god life despite being raised by a teen parent. I just wanted to get that out of the way before people started badgering me on something they don't know anything about. Now back to the topic at hand! My doctor ordered an amniocentesis (not sure why ... i didn't ask) and discovered that my baby has a chromosome defect called Trisomy 13. Infants with the illness are not expected to go home from the hospital. He told me I had an option to terminate the pregnancy. I don't know what to do, I love my baby so much already but I don't want to have her knowing she won't be with me for the rest of my life. I feel like I'm being selfish about the situation but it is really making me depressed =( what are your opinions on ending a pregnancy due to a situation like this? Thanks for your time!