The elf-ogre hybrid from Mystara was called the Ndjatwa --- however, they were a magical fusion (the gods must be crazy).
The numbers being bandied about are basic genetics (the ratios look like those derived from a Punnet square). Someone pointed out that this situation is one of blending, which I would tend to agree with. The easiest thing to do is assume that there *is* a chance of miscarriage, and a high probability that any surviving child is basically human. After all, the D&D world is chock full o' humans and this might be why... Of course, you could allow the child to take a bloodline (see Unearthed Arcana), or create for it 'feats of the blood' based on Snake Blood (FRCS) and Orc Blood (Dragon 315, Regional Feats of Oerth).