Rashi on Leviticus 12:2/רש"י על ויקרא י״ב:ב׳

1אשה כי תזריע IF A WOMAN HAVE CONCEIVED SEED — R. Simlai said: Even as the formation of man took place after that of every cattle, beast and fowl when the world was created, so, too, the law regarding him is set forth after the law regarding cattle, beast and fowl (contained in the previous chapter) (Leviticus Rabbah 14:1).

2כי תזריע — These words are superfluous, כי ילדה would suffice — they mean literally, ”if she bringeth forth seed” and are employed to include the case that if she gave birth to him (the male child) as a pulpy mass which had dissolved, having become liquified like seed, even then its mother becomes unclean as though it were a normal birth (Niddah 27b).

3 כימי נדת דותה תטמא AS IN THE DAYS OF THE SEPARATION FOR HER IMPURITY SHALL SHE BECOME UNCLEAN — According to the regulation of every uncleanness which is mentioned in the case of a נדה does she become unclean in respect to the uncleanness resulting from child-birth — even though the womb opened without any issue of blood (cf. Niddah 21a).

4דותה — This is an expression for anything which flows from her body (‎‎‏זב = דו, “flowing”), and the translation is: “as in the days of separation due to her flux”. Another explanation is: it has the same meaning as .מדוה (root דוה), malady and sickness, and this is termed דותה, “her sickness”, because no woman sees an issue of blood from herself except that, as a result of it, she becomes unwell and her head and limbs feel heavy (cf. Niddah 9a).