"And when the days of her purification are fulfilled, for a son, or for a daughter, she shall bring a lamb of the first year for an Olah, and a young dove, or a turtle-dove, for a Chatos." Why does a woman who gave birth have to bring a Korbon Chatos - a sin offering? What sin has she committed to require her to bring such a Korbon?
Some Meforshim explain, "Since during her labor pains, she might have made an oath to never have another baby, she therefore brings a Korbon to atone for that oath and nullify it."
Kli Yakar offers a different explanation. He says, "The atonement is not for this woman, but rather for Chavah - the first woman. Since pain from pregnancy and labor is a punishment for Chavah's sin, eating from the Aitz HaDaas, this woman brings a Korban now to atone Chava's sin. After going through all the pain of her pregnancy and labor she wants to bring an end to this suffering and brings a Korbon for Chava's Avayra."