Sforno on Leviticus 12:2/ספורנו על ויקרא י״ב:ב׳

1אשה כי תזריע וילדה זכר, the sages in Niddah 31 explain the term תזריע in our verse as “when a woman experiences her orgasm before her male partner the child born from such a union will be a male. The perception underlying this is that the woman’s “seed” is the moisture which she excretes from time to time at the time she engages in physical union with her partner does not enter into the formation of a male embryo. Her “semen” is active in suppressing the effect of the man’s semen. But her blood enters the semen of the male it moistens and provides addition impetus to the man’s semen,

2כימי נדבת דותה, for during the first seven days after her giving birth she is like a menstruating woman regarding her ritual status.