knowledge is power.
if you are adamant that despite the results you would not choose terminating the pregnancy, and would raise the child yourself-knowing of any potential medical issues ahead of time can provide you time to educate yourself and your family about what to expect.
in the event that there are issues that may endanger your life, or may impact on the baby's chance of survival, in my opinion, you have to take the necessary steps to ensure your safety-and prepare your current children should you not be bring a sibling for them home from the hospital.
one of my former co-workers opted to not have any testing done because she was adamant against terminating any kind of pregnancy. the two children she had already eagerly anticipated their new sibling and were very emotionaly invested in it's arrival. sadly, the child never had a chance. the little girl was born without ever having developed a brain and a large portion of her skull-it was a condition that would have been picked up very clearly in something as simple as a sonogram. to complicate matters the delivery was very bad and the mother greatly endangered her life (doctors told her later had they known of the child's condition it would have been a mandatory c-section to ensure her safety). on top of recovering physicaly, and emotionaly-the mom was left to deal with 2 young children that could not fathom why mom had'nt brought home the baby she 'promised', and why mommy had left them to stay in the hospital for so long. a few years later when she became pregnant again it was an ordeal with the children greatly fearful for her safety and not willing to hear any talk of their impending sibling-the did'nt belive it was going to happen based on past experience and they were'nt going to trust being saddened and disappointed again
in hindsight she was adamant that while she would not have terminated her pregnancy she would have wanted to know so she could have prepared the children for the actual realities of the known outcome. she also would have taken the necessary steps to ensure her own safety.