If you want to keep the marriage intact, you may just have to accept that it's up to you to raise the kids. Some men (and women) are just not up to the task. They try, but they just can't dredge up what it takes to be a hands-on caregiver.
There doesn't seem to me to be *too* much reason for your husband's distress over having a third child since as you describe it he isn't fully involved in the household and parenting as it is. And this is even considering that you are also working. Does he know that you also have ambivalent feelings about this? If you are friends, lovers, and true partners, even if he deep down doesn't want this child (or even, I'm sorry to say, quite up front, since he is making appalling comments about miscarriage) then he should at least support *you* as you carry and raise this child (and the others). He may not do a great job of actually running the household or raising the kids, but if he can't even commit to you, as you are (pregnant and optimistic), and accept your fears, hopes, and struggles with an eye to a lifetime together, then that looks like trouble to me.
Have you talked to him quite frankly that no matter his thoughts and feelings on the issues, this is going to happen and that you expect him to give his love and support to the best of his ability. This means no more whining or miscarriage jokes and to pull his weight in the household (you may have to specify). You are both adults and you have a job to do and that's just how it is. We don't always like or want what life hands us but we can accept it and meet it with equanimity and our best effort.
Parenting is often not very good for marriages. Some marriages survive and some don't. I had to accept my husband's limitations (and they were significant) because I love him and I know that he did what he could. Now that we have an empty nest we are very happy together. Parenting was not our best episode. But at least we pulled in the same direction and didn't doubt the commitment of one another.
It's also possible that that your husband's attitude will change once the baby is born and he bonds with him/her. But even if it doesn't he should still do his best by his family, daily. You could let him know that this is OK and that you want to do this together.