“Bechor peter rechem” means the first child (and only if that child is male)exiting through natural, non-surgical means through the womb. If there was a miscarriage, then THAT child was the bechor (According to everything I always learned), though in most cases people do not know if the blighted pregnancy was a male or female. A pidyon is not required for a c-section first-born male. In the case of a V-BAC male infant, I believe it is required.
