It's a fine line to walk. Here's the thing, I fully believe in providing full support, care and love to any child. But there's also a serious reality. Life is going to be really hard for a child with down's syndrome and also for his or her caregivers. It's a difficult decision, but termination of the pregnancy is the best option here.
I feel that knowingly giving birth to a mentally disabled child is unfair and selfish in several ways. Firstly, it is unfair to bring a life into the world knowing that it destined for an unfulfilled life. Secondly, it is unfair to society at large, which will have to take on the responsibility of caring for and supporting the child. Thirdly, I would not want to burden my friends and family with having to help care for a disabled child.
Yes, I would terminate the pregnancy if the baby was diagnosed with Down's Syndrome because the child will forever be a burden to the parents because the require constant guidance and attention. Although the practice of terminating pregnancies are viewed as wrong and immoral by many people, I believe that it would be better to terminate the pregnancy because of the problems involved in the future.
Without knowing the specific timeframe for when the fetus can be diagnosed with down's, I cannot give a solid answer. However, I think it would be a great challenge for myself, my husband, and the child him or herself. I believe if I knew that this was likely before the fetus became fully viable outside the womb, I'd seriously consider the option. If the baby was fully viable outside the womb, and fully developed, I'd say that'd basically be murder, and would not terminate.