2,126. An Aborted Fetus and Birth Impurity
Hilchos Issurei Biah 10:6
If a fetus is cut up inside the womb, the woman is not rendered unclean until the greater part of the body emerges. The is true regardless of whether the limbs came out in their usual order – e.g., foot, calf, thigh, etc. – or in some random fashion. If the whole head emerges intact, it’s as if the greater portion of the body has emerged. If the fetus wasn’t cut up and it emerged in the normal fashion, it’s considered born once the forehead emerges. This is so even if it was subsequently cut up.
Hilchos Issurei Biah 10:7
If a fetus sticks a hand out and pulls it back in, the mother is unclean from birth impurity by rabbinic enactment. She doesn’t have pure days until the entire fetus emerges, or the greater part of it, as has already been discussed.