The doctor is not God. He or she doesn't know everything.
I was seven months pregnant with my first child when my former OB/GYN told me that I had to abort because my test results came back showing that my unborn son had Downs Syndrome. The OB/GYN proceeded to lecture me about how it would be humane for me to abort my son rather than allow him to be born with Downs. I was then fervently told that my son would be up against great odds if he was born and it would be extremely expensive for my husband and I to care for a Downs child.
Of course, I outright refused to abort my unborn child and I gave birth to a HEALTHY baby boy, who is now 25 years old. My son didn't have Downs Syndrome as the medical doctor insisted that he did.