Parashas Metzora · Passuk 15:25
Chabad.org — English translation + Rashi
Torah Temima points to Toras Kohanim.
English: “When her blood flows” — the Rabbis taught: her blood on account of herself, and not on account of a child [i.e., labor pains in the days of zivah do not create zavah impurity].
Exclusion of labor-related blood in zivah days
Chazal exclude blood caused by the hardship of childbirth during zivah days from establishing zavah status.