Although many of the problems faced by the female athlete affect the male athlete as well, some occur exclusively or more commonly in women. These include spondylolisthesis, stress fractures in the pelvis and hip, and pelvic floor dysfunction. Female athletes are also more likely to have patellofemoral problems, noncontact anterior cruciate ligament tears, and bunions. For many of these conditions, the relative influences of osseous anatomy, ligamentous laxity, and the effect of sex hormones have not yet been established. There are also problems related specifically to the menstrual cycle and pregnancy. Amenorrhea is present in up to 20% of vigorously exercising women. The term "female athlete triad" has been coined to describe the complex interplay of menstrual irregularity, disordered eating, and premature osteoporosis seen in the female athlete. Many of the concerns related to exercise during pregnancy focus on the safety of the fetus rather than the athlete herself. Musculoskeletal problems in the physically active pregnant woman are related to weight gain, ligamentous relaxation, lordosis, and change in the center of gravity.