According to the Torah, when a woman gives birth – whether to a male child or to a female child, and even if the baby is stillborn or if the woman miscarries – she is rendered ritually unclean with tum’at leidah – the impurity of birth (see Vayikra 12:1-5). Since this rule is only true if there was a birth, yet it also encompasses miscarriages, the Sages need to define what constitutes a birth. The third perek of Massekhet Nidda, which begins on today’s daf deals with these issues.
According to the Mishna:
If a woman aborted a shapeless object, if there was blood with it, she is unclean, otherwise she is clean. Rabbi Yehudah ruled: in either case she is unclean.
If a woman aborted an object that was like a rind, like a hair, like earth, like red flies, let her put it in water and if it dissolves she is unclean, but if it does not she is clean.
If an abortion was in the shape of fishes, locusts, or any forbidden animals or creeping things, if there was blood with them she is unclean, otherwise she is clean.
When the Mishna teaches that in cases where there is blood accompanying the birth the woman is deemed to be ritually unclean, it does not make clear what type of tum’ah the woman is understood to have contracted. Rashi says that since the woman bleeds, it is understood to be a menstrual flow and she is considered to be a nidda, which requires a seven day wait before performing the purity ritual. Some point out that the laws of nidda only apply at certain times during a woman’s menstrual cycle, so that if the miscarriage takes place at other times, the woman must be viewed as a zava whose requirement is to wait only yom k’neged yom – one day for every day that there is bleeding – before the ritual immersion can take place.
In his Commentary to the Mishna, the Rambam points out that this is only true if the shapeless object does not contain a bone. If it does contain a bone then we view the miscarriage as a birth, and the woman has tum’at leidah according to the rules set out in Vayikra (12:1-5).