Well, we've already left real-world biology far, far behind. But, let's just pretend. . . .
This individual gets his (I'm assuming the baby will be a boy, no need to do this of course) genes from 4 grandparents. For now, let's assume the distribution is equally likely. The baby's maternal grandparents are an elf and a human, the paternal grandparents are an ogre and a human. I'm going to guess that the half-elf's father was human and the half-ogre's father was human, though this may not be the case either.
.................................Paternal......................Paternal
.................................Grandmother................Grandfather
Maternal grandmother...1/2-elf, 1/2-human.........1/2-ogre, 1/2-elf
Maternal grandfather....1/2-human, 1/2-human....1/2-human, 1/2-ogre
So, there's a 25% chance the baby is a human, a 25% change the baby is a half-elf (though with a different mix of genetic characteristics than the half-elf parent), a 25% change the baby is a half-ogre (again, with a different mix of genetic characteristics than the half-ogre parent), and a 25% chance of an elf-ogre. I suppose you could argue that elves and ogres can mix, and so there's basically a flat 25% chance of miscarriage. But, you could always allow it and then come up with a new racial mixture.
Dave