"Women with irregular periods sometimes seem to get more regular after pregnancy," Wood says, "although I don't know of any studies to back this up." Certainly, it's common for women to report that their menstrual cramps diminish or vanish. This may be because the uterus gets stretched out or because pregnancy reportedly decreases the number of receptor sites for prostaglandins, your body's cramp-triggering chemicals. If you had endometriosis, which can make periods extremely painful, nine or more months without periods can clear up many of the lesions, banishing endometriosis for at least a while. Another bonus: Endometrial and ovarian cancer risks generally go down after pregnancy, and breast-feeding strengthens the effect further, according to the American Cancer Society.