Midrash su Levitico 12:5

1) (Vayikra 12:5) "And if a female she shall bear": This tells me only of (a child that is clearly) a female. Whence do I derive the same for one whose sex is in doubt and for a hermaphrodite? From "she shall bear." The criterion (for what follows) is the bearing (And since the sex here is in doubt, we assign her the days of cleanliness for a male, and the days of uncleanliness for a female.) "then she shall be unclean shvuayim": two weeks, fourteen days.

2) R. Yehudah b. Roetz was asked by his disciples: We hear "shivim" ("seventy," for we follow the written form [without a vav after the beth]). Is it possible that she is unclean for seventy days? He answered: "Tumah" and "taharah" (cleanliness) are mentioned both in respect to a male and in respect to a female. Just as the days of her taharah (sixty-six) are double those for a male, so the days of her tumah (fourteen) are double those for a male. After they left, he went after them and said to them: What I told you was not really necessary, for we follow the spoken form (and not the written), but this is the reasoning behind it: "Tumah" and "taharah" are mentioned both in respect to a male and in respect to a female. Just as the days of her taharah are double those for a male, so the days of her tumah are double those for a male. — But perhaps go in this direction: A male, whose days of taharah are few (thirty-three), its days of tumah are few (seven). A female, whose days of taharah are many (sixty-six), how much more so should its days of tumah be few! It is, therefore, (to negate this) written: "then she shall be unclean shvuayim" (the spoken form), two weeks, fourteen days.

3) (Vayikra 12:5) "and sixty days, etc.": I might think, either consecutive or scattered; it is, therefore, written "sixty day" (lit.) — Just as one day is consecutive, so are sixty. I might think that the sixty are consecutive, but the six may be either consecutive or scattered; it is, therefore, written "and sixty days and six days." — Just as the sixty are consecutive, so the six are consecutive. Why need "sixty-six days" be written? (I would know that it is double the thirty-three of a male.) (For I would reason:) If for a male, for which the days of uncleanliness are few (seven), the days of cleanliness are few (thirty-three), then for a female, for which the days of uncleanliness are many (fourteen), how much more so should the days of cleanliness be few. It is, therefore, written "and sixty-six days she shall abide."