cat I haven't yet been moved to post on mumsnet but I couldn't let your post pass by. I'm so very sorry for your situation.
I'd neither categorise myself as pro life or pro choice, and I've not been in your situation, so not much good to you. However I am a Christian, and I also carry a genetic disorder which if passed on would mean very not good things for my potential child. My great grandmother had three such children (we assume same disorder), and all three died in early childhood. There is not the complicating risk to maternal health or constant pain to the child that you describe. My great grandmother was a Christian and married to a church leader; according to my grandfather (her son) she would have terminated her children had the option been available. Apparently she told my grandad that had she known she would have not had any children.
I have only a risk of 1/16-1/20 per pg of a child inheriting that disorder, but that was enough for me to decide I would not be able to bear children naturally. The deciding factor for me was the thought of looking that child in the eye as they went through surgery after surgery without being able to understand why, and trusting me implicitly, while all the while I would know I had chosen that life for them. A few years after I made the decision not to have biological children, we found out about IVF PGD and went down that route instead.
That is a decision I struggle with daily. I feel on the defensive with Christian friends as I suspect them of judging me, but i do share the choice we made as I feel it's important to do so. I also struggle to feel peace in the decision, I don't know whether we did right by God or not, and I wouldn't want to speak for him.
However this is how I process our decision and I hope (although doubt) that if I did encounter a vehemently pro life person in RL I would be able to share some of this.
Through my experiences within the online community for my particular condition, I have begun to believe that it is possible & indeed most likely that there is not a blanket rule regarding these situations, but that God works with each of us as individuals, taking into account our circumstances. I believe he speaks into our hearts and guides us via the holy spirit, taking into account everything else within our lives & his knowledge of the future.
No one I know has ended a pregnancy flippancy and all of them have done so out of love.
I know women who are loving and devoted parents - a level of love & devotion I can't fathom, personally - and yet still say that they would terminate in the same situation again. Equally I have seen women carry to term & have babies much healthier than expected.
God himself in the form of Jesus was intimately involved with suffering and took pains to end physical suffering when asked to do so, in a way that was above & beyond his 'call of duty'. It seems to have been of great importance to him and he displayed a lot of compassion for those suffering. He himself took on terrible suffering in order to ease our suffering. In that way I think he could be compared to a parent who chooses to take on the guilt and sadness of termination so that their child doesn't suffer.
Through the online community, I have seen pro lifers terminate, and I have seen pro choicers refuse all testing. This makes me realise that I can never know what I will do unless I am faced with that decision.
It really bugs be that on this thread there are people commenting that you should terminate - pro choice should be just that, open minded & supportive. If one is pro abortion then don't claim to be pro choice. The choice should be the parents, and nobody else's. Guilting somebody into terminating is as bad as guilting somebody into carrying to term.
Good luck OP and much, much luck. I'm glad you have made a decision you seem comfortable with, and I pray that things go better than expected with your in laws. Good luck :-)