That's a woman though, a cat's system is much different- in a colony outside, many females will be mated with more than once, producing a large litter of kittens, but those that are fathered by one tom, will smell different to the mother than those fathered by another. In a colony, sometimes one tom will come to the litter and sniff out his kittens. He may then (though this is rare) choose to help nuture the kittens to take the load off of mom. But, he will also attempt to kill the other kittens that are not in his group. So the momcat will generally chase him off to protect her brood. Since these kittens are conceived at different times, this leaves the last litter at the mercy of the first- when the contractions start, no matter in what stage of developement the last litter is, they too are pushed out in the world. That's why in some cases in what looks like a perfectly healthy vibrant litter of kittens you may also have runts, or premies.
That's why controlled breeding is so important, because in some cases, depending on the cross breeds of the outside cats, blood types don't match on the parents and the kittens are born genetically altered, or ill. With ethical breeding, and the study of blood lines, this tragedy is often averted because special attention is paid to the queen and the tom as well in order to produce the strongest and best kittens in the line.