I have no desire to stumble into a moral or religious discussion, but would like to raise one point that might possibly be relevant. As most members know, in the U.S. Census in 1900 and 1910, married women were asked to report how many children they were mother of and how many were still living. I have found more than a few of these records that aren't consistent with other data about the family -- for example, a woman reported that she was mother of 8 children, 6 living, and I have profiled the six, but found no record of the other two. I suspect that they may represent miscarriages or stillbirths, but I have no data to corroborate that. And so I just enter a comment on the mother's biography saying that she reported eight children, but I have found no records for two of them.
The point I'm working my way to is this: in a situation where a medical or family record, or some other record, might exist that could be found by a future genealogist, and that could create uncertainty or confusion about the size of a family, I think it would be OK to include a brief clarification or explanatory statement in the mother's profile, if you have personal knowledge of it. It might not be necessary to provide all the details, and I certainly wouldn't create a profile for the unborn. But let's face it, many of our medical records are now online, and I don't think we really know how well protected they are.