Why does the Church baptize boys after 40 days, and girls after 80 days?
The Church can baptize any newborn child boy or girl on any day without waiting forty or eighty days. The forty or eighty–day-waiting period is the required time before the mother, who is the God mother, is allowed to participate in her child’s baptism. For God commanded Moses saying, "If a woman has conceived, and borne a male child, then she shall be unclean seven days; as in the days of her customary impurity she shall be unclean. 'And on the eighth day the flesh of his foreskin shall be circumcised. 'She shall then continue in the blood of her purification thirty-three days. She shall not touch any hallowed thing, nor come into the sanctuary until the days of her purification are fulfilled. 'But if she bears a female child, then she shall be unclean two weeks, as in her customary impurity, and she shall continue in the blood of her purification sixty-six days" (Lev 12:2-5).
Forty days is considered an enough period for the postpartum hemorrhage to stop. The doubling of the periods when a female is born is intended to remind us of the fact that the woman was the first to fall into temptation and to introduce sin to the world (1 Tim 2:13-15; 1 Pet 3:7).