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 leida – the impurity of a woman after childbirth (see 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 discharges an amorphous piece of tissue, if there was blood with it, she is ritually impure, otherwise she is pure. Rabbi Yehuda ruled: in either case she is impure.
If a woman discharges an item similar to a shell, or similar to a hair, or similar to soil, or similar to mosquitoes, if such items are red she should cast them into water to ascertain their nature: If they dissolve, it is blood and the woman is impure, but if not she is pure.
If a woman discharges an item similar to a fish, or to grasshoppers, repugnant creatures, or creeping animals, if there is blood that emerges with them she is impure, and if not, she is pure.
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 amorphous tissue 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 leida according to the rules set out in Vayikra (12:1-5).