Deepest sympathies from me. As you can probably tell, ENWorld is grieving with you.
All the best to you and your daughter and Melody. Death is of course hardest for those who are left behind. I pray for a miracle - let it be any of the following, as God wills...
1.) The self-correction of the problem that is plaguing your daughter, her recovery, birth, and normal life.
2.) That if the baby passes away, you and Melody will feel the peace and comfort that (a) you did the best you could, (b) for whatever reason, her time on earth was to be exceedingly short, and/or (c) she is in a place where her defects will never manifest themselves and she can be happy.
3.) That your daughter will survive, and despite problems due to the complications in the pregnancy, you and Melody are able to see her and hold her and love her and raise her for whatever period of time God chooses to give her.
While trying to avoid anything too religious here (I know it's flamebait), let me state that I believe God has a special place reserved for those children he allows to return home early... and for the parents who are strong enough to let them return to him... and that he did have a purpose in mind for you and Melody with the pregnancy. And I believe that your talking and singing and such to your daughter did in fact help her and teach her something.
As a father of two, my heart aches for you, Mistwell. I can imagine what it would be like to lose a child (as I detailed before, we had a couple of close calls). It boils down to:
"No parent should ever have to bury a child."
--Theoden, Peter Jackson's The Two Towers