Catholic doctrine states that baptism washes away sin including original sin. Well, periods and pains related to child birth are the punishment for original sin, at least for women. Why are we still being punished for a sin that is washed away?
The Catechism is not exactly a clear to get an answer to this question. Although the Bible says that pain during childbirth is a punishment (as well as man's toil, which I can attest to and woman being subjected to her husband, which I can't exactly attest to but I've heard things about in antiquity).
Although it is proper to each individual, original sin does not have the character of a personal fault in any of Adam's descendants. It is a deprivation of original holiness and justice, but human nature has not been totally corrupted: it is wounded in the natural powers proper to it, subject to ignorance, suffering and the dominion of death, and inclined to sin - an inclination to evil that is called concupiscence". Baptism, by imparting the life of Christ's grace, erases original sin and turns a man back towards God, but the consequences for nature, weakened and inclined to evil, persist in man and summon him to spiritual battle
CCC - 405
The fruit of Baptism, or baptismal grace, is a rich reality that includes forgiveness of original sin and all personal sins, birth into the new life by which man becomes an adoptive son of the Father, a member of Christ and a temple of the Holy Spirit. By this very fact the person baptized is incorporated into the Church, the Body of Christ, and made a sharer in the priesthood of Christ.
The Bible does not say what the effect of Sanctifying Grace is and freedom from original sin is, other than being able to live forever in heaven, which is worth all the pain and toil in the world.
The fact is, that you still have, in addition to the aforementioned curses as a result of original sin, something called concupiscence
Etymologically, "concupiscence" can refer to any intense form of human desire. Christian theology has given it a particular meaning: the movement of the sensitive appetite contrary to the operation of the human reason. The apostle St. Paul identifies it with the rebellion of the "flesh" against the "spirit." Concupiscence stems from the disobedience of the first sin. It unsettles man's moral faculties and, without being in itself an offense, inclines man to commit sins.
CCC - 2515
And concupiscence is what mainly separates someone who is free original sin (like Our Lady and Our Savior) and the rest of us.
The big question is, whether the Blessed Virgin Mary had pain during childbirth, and several mystics and theologians posit that she did not.
If baptism washes away original sin, why do women still get periods and pain?
Baptism removes both Original Sin and actual sin from our souls.
Let me point out first the aspect of what Baptism does. The Catechism of the Catholic Church states:
1263 By Baptism all sins are forgiven, original sin and all personal sins, as well as all punishment for sin.66 In those who have been reborn nothing remains that would impede their entry into the Kingdom of God, neither Adam's sin, nor personal sin, nor the consequences of sin, the gravest of which is separation from God.
1264 Yet certain temporal consequences of sin remain in the baptized, such as suffering, illness, death, and such frailties inherent in life as weaknesses of character, and so on, as well as an inclination to sin that Tradition calls concupiscence, or metaphorically, "the tinder for sin" (fomes peccati); since concupiscence "is left for us to wrestle with, it cannot harm those who do not consent but manfully resist it by the grace of Jesus Christ." Indeed, "an athlete is not crowned unless he competes according to the rules."
So the Catechism of the Catholic Church admits that ”certain temporal consequences of sin remain in the baptized, such as suffering, illness, death, and such frailties inherent in life as weaknesses of character, and so on, as well as an inclination to sin.”
Thus women having periods and pain in childbirth are not removed by baptism.
Besides pain in childbirth is a punishment handed out to mankind as result of our parents first sin.
16 To the woman also he said: I will multiply thy sorrows, and thy conceptions: in sorrow shalt thou bring forth children, and thou shalt be under thy husband's power, and he shall have dominion over thee. - Genesis 3:16-17
Baptism does not reduce the terms of our existence which he has imposed on humanity. Furthermore, Scriptures state that God ”would greatly increase woman's pain during childbirth” and not that it was not already part of the original plan involving humanity in general.
While we may see the pain in childbearing and the toiling as punishments, these are also very important in teaching us to be holy. Just like being sent out of Eden wasn’t a punishment but rather God’s grace, as we would have become like Satan if we had eaten of the tree of life.
Pain and work teach us to trust in God and in each other. They also help us value the fruits of our labour. Remember baptism doesn’t make us holy automatically, it forgives us our sins and allows us to approach God. But we must constantly work towards sanctification in our lives, and all the trials and tribulations we face can build us up and bring us closer to holiness.