Niddah 3:4

If a woman miscarries something that resembles a sandal or a placenta, she must observe both the procedure for after delivering a boy and the procedure for after delivering a girl. If there’s a placenta in a house, the house is ritually unclean. This isn’t because a placenta is a fetus, it’s because there’s no placenta without a fetus. Rabbi Shimon says that the fetus was absorbed within the placenta before it came out.

Niddah 3:5

If a woman miscarries a hermaphrodite or a fetus of indeterminate gender, she must observe both the procedure for after delivering a boy and the procedure for after delivering a girl. If she miscarries both a male and a hermaphrodite or both a male and a fetus of indeterminate gender, she observes both the procedure for a boy and for a girl. If she miscarries both a female and a hermaphrodite or both a female and a fetus of indeterminate gender, she only observes the procedure for a girl. If a fetus comes out in pieces or backwards, it is considered delivered once the greater part of it has come out; if it comes out in the normal fashion, it is considered born once the greater part of the head emerges. By “the greater part,” we mean the forehead.