During early stages, there is no indication which gender is present but through DNA testing. There are no developed complexes for the brain, nervous system, etc. Quite simply, and somewhat sadistically, the fetus cannot 'feel' in a very young state. After a certain point, it is brutal to kill a young child capable of living on it own, outside the mothers womb.

__________________
"Gimme some truth, now whose side are we on? Whatever you say, turn on the boob tube I'm in the mood to obey" Jack Johnson