Chulin 4:2-3

Chulin 4:2

[Firstborn animals are sanctified from the time that their major portion emerges from the mother.] If an animal was having a difficult labor with its firstborn offspring, then the young’s limbs may be severed one at a time and thrown to the dogs. Once the major part of the offspring has emerged, it must be buried (because of firstborn sanctity) and the subsequent animals born from this mother are exempt from the law of firstborn animals.

Chulin 4:3

Let’s say that an animal’s fetus died in the womb and the shepherd stuck his hand in and touched it. Regardless of whether it was a kosher or non-kosher animal, he remains ritually clean. Rabbi Yosi HaGlili says that if it is a non-kosher animal, he is ritually unclean; if a kosher animal, he is ritually clean. If a human fetus died in the womb and the midwife stuck her in hand and touched it, she is ritually impure for seven days but the mother remains ritually clean until the fetus emerges.