Coffin Birth? Never heard that one before and considering that the baby relies on the mother for oxygen....
In doing some more research on this topic I found that there are various theories on this subject which mainly focus on the mother's own body (While decomposing after death) forms gasses that basically expel the unborn baby from the womb.
For more details please see ABC NEWS: Source
Have you heard about this before?
One would think such a phenomenon would have a very small window of probability. A fetus relies on the mother's circulatory system and respiratory system to such a degree that when the parent's blood stops bearing oxygen and the baby's own system has to take over, the chance of a successful birth being achieved must be astronomically unlikely. The baby would have to be extremely late-term, and would probably have some sort of disability afterwards. The whole thing sounds like something out of Poe or a Shakespeare tragedy to me.