Mias - not sure if this is any help at all, but when I was 6 weeks pregnant with my first little boy (who is now 5) my mum died. I couldn't believe the timing of it, and couldn't have imagined a worse time to be pregnant. It was awful, my morning sickness was really bad around the funeral and I remember throwing up in tears trying to get ready for it. I didn't eat, slept all day and was awake all night, and didn't even bother going to see a midwife until I was nearly 12 weeks pregnant as couldn't face it. I was sad all the way through and found no joy in it at all, I almost felt embarrassed that it was happening when everyone was in the midst of terrible grief. I remember having to tell all my family and kind of apologised whenever I told anyone. (They were all fine with it, it was my issue) I was devastated at the 12 week scan as was in the waiting room with loads of mums and daughters, and remember that the 20 week scan wasn't much better. I couldn't bring myself to go shopping or get ready for him in any way. Then, at about 36 ish weeks I went into a frenzy and actually have happy memories of that. The day he was born was also ok, and it was more the anticipation of not having her there.
Anyway, point being that my little boy is a lovely, balanced, happy little person - and the same could be said for my subsequent children who were born in happier circumstances. I also had the same worries as you, but I did find that once he was born I had a happiness that I didn't think would have been possible, and although there has been a lot of sadness for me over the last years, he has balanced that out.
Now trying to get pregnant again after loosing my 3 year old I am in the same situation as you, and I have faith that the baby will come through it fine, and as with everyone else, represents some hope for my future, that I am actually going to want to stick around for my future - and I am sure that the pregnancy will have no baring on that, and am hoping that once I have a baby, the sadness will sit with the happiness like it has done before. Obviously the death of a parent and a child is different, but as I have now experienced both, I am seeing that my grief pattern is the same, just harder for my child. I am hoping that if I do have another baby soon, the sadness will sit with the happiness and will not have an adverse effect on the child. xxxxx