Define “period”

Q: My question is about my girlfriend’s period. When should it start? When should it end? What is the connection to pregnancy?

Dr. Klein: During a typical month, the lining of a woman’s uterus grows thick with the nutrients a fetus would need if one were conceived. At the end of the month, if no fetus has been conceived, the body eliminates this uterine lining of tissue and blood. The several days that this elimination occurs is called a woman’s period. If a woman is pregnant, the body needs this rich uterine lining, and so it is not eliminated, and there is no period. Each woman’s period starts and stops on her own schedule; the whole cycle typically lasts between 24-34 days.