Leviticus 12: Birth Day

“On the completion of her period of purification, for either son or daughter, she shall bring to the priest, at the entrance of the Tent of Meeting, a lamb in its first year for a burnt offering, and a pigeon or a turtledove for a sin offering (verse 6: וּבִמְלֹאת יְמֵי טָהֳרָהּ לְבֵן אוֹ לְבַת תָּבִיא כֶבֶשׂ בֶּן־שְׁנָתוֹ לְעֹלָה וּבֶן־יוֹנָה אוֹ תֹר לְחַטָּאת אֶל־פֶּתַח אֹהֶל מוֹעֵד אֶל־הַכֹּהֵן׃).
Why does the woman have to bring a sin offering after giving birth? This seems antithetical to the Torah commandment to be fruitful and multiply? One school of thought is that the sin offering is meant to atone for anything the woman might have said during the pangs of childbirth. Ibn Ezra believes this is for generic unseemly things that she may have yelled. Rabman, quoting the Gemara, focusing on a more specific pronouncement. During childbirth, the mother may have sworn that she would never sleep with her husband again to avoid having to go through childbirth again. The Kli Yakar takes a different approach altogether. The sin offering is part of the atonement process for the sin of Eve. After Adam and Eve ate from the tree of knowledge, God punished Adam that he would have to till the soil to get food and Eve that she would have pain in childbirth. The Rav offers a slightly different version of this idea. The connection to Eve is not to the sin offering, but to the time the mother must wait in a state of impurity. Adam and Eve could not wait a few hours until they ate from the tree of knowledge. Therefore, a mother must wait a certain period of time after giving birth before she can be pure again. It is interesting that the father has no part of this chapter at all. It's possible that the Torah established this time period of impurity in order to protect the mother. By forcing her to sit out, it allows the mother to heal from the delivery. There difference in the waiting time between a boy and a girl seems to be rooted in ancient views of boys verses girls. Many of the medieval commentaries offer various explanations based on gestational science at the time, like female briths caused the mother to bleed more. This hints at a possible patriarchal view of the difference between boys and girls as a source for the length of time. The Netziv, however, offers a slightly different view. He explains that baby boy should have had the same length as a girl, but the fact that a baby boy will have a brit milah eight days after he is born cuts the time shorter for the mother.