The Torah establishes in Parashat Tazria (Vayikra 12:2-5) that a woman who delivers a child becomes Teme’a (“impure”). This status results in a prohibition against marital relations, and a prohibition against entering the Bet Ha’mikdash and against partaking of hallowed food (such as Teruma and the meat of sacrifices). The woman remains Teme’a for seven days after delivering a boy, and for fourteen days after delivering a girl.
The Sefer Ha’hinuch, in discussing this Misva, presents his theory regarding the concept underlying the status of Tum’a resulting from various bodily discharges. He writes that when the body is ridding itself of some excess material, this signifies that it is not perfectly healthy. We know this, of course, from medical phenomena such as nasal congestion and a loose bowel; excessive discharge indicates that the body is in a compromised condition. During menstruation, too, a woman generally feels weak and unwell. Therefore, the Torah determined that certain bodily discharges – including childbirth, whereby an entire organism is expelled from the body – bring upon a person the status of Tum’a. As this person is in a compromised physical condition, he or she is considered “impure” so that others will keep their distance. Marital relations, of course, constitutes the closest form of physical contact between people, and so the Torah forbade relations during the wife’s period of Tum’a.
As for the difference between the birth of a boy and the birth of a girl, the Sefer Ha’hinuch suggests that the birth of a girl signifies the mother’s tendency to have a higher body temperature, whereas the birth of a boy indicates her tendency to have a lower temperature. Excessive body heat, the Sefer Ha’hinuch writes, is more debilitating than insufficient body heat. Therefore, after the birth of a girl, which indicates a tendency to have a higher body temperature, the mother generally requires a longer period of recovery than after the birth of a boy. For this reason, the Torah established a longer period of Tum’a after the birth of a girl than following the birth of a boy.
The Rebbe of Kotzk (Rav Menachem Mendel Morgenstern, 1787-1859) offered a different approach. He explains that Tum’a results from the loss of Kedusha (sanctity). For example, the most severe form of Tum’a is that generated by a human corpse, because a living human being possesses a sacred soul, and thus the loss of that soul creates an enormous vacuum. This vacuum is the source of Tum’a, and the larger the vacuum is, the more severe the Tum’a is going to be. After childbirth, the Rebbe of Kotzk explained, the woman’s body loses something sacred and precious – a human organism – and she therefore becomes Teme’a because of the vacuum which is created. As females are capable of delivering children, a female fetus is considered significantly holier than a male fetus, and thus the delivery of a girl generates a higher level of Tum’a than the delivery of a boy, because a larger vacuum is created after a girl leaves the woman’s body.
The Sefer Ha’hinuch here also advances a number of theories to explain the reason why G-d created women such that they experience the monthly cycle of menstruation. First, he suggests, women tend to be more emotional, which could lead them to act rashly. The monthly discomfort of menstruation has the effect of helping to reduce their haste and impulsivity. Secondly, he writes, the Torah wanted to create a regular period of distance between a husband and wife in order to maintain their desire for one another. If there was never any period of separation between a husband and wife, they would become too accustomed to one another, and their interest might then be drawn to other people.
A woman becomes Teme’a at childbirth even if no blood appears to leave the body. As the Gemara states, “En Petihat Ha’keber Be’lo Dam” – the uterus does not open without at least some bleeding. Therefore, even if no blood is seen, the woman becomes Teme’a at childbirth.
A woman becomes Teme’a even after a miscarriage, Heaven forbid.
Needless to say, this Halacha applies at all places and at all times, even after the destruction of the Bet Ha’mikdash.