If you never menstruate, ovulation is not occurring and conception would be difficult without intervention. This can be common in women who are considered underweight by body mass index (BMI) standards. The body requires a certain level of body fat for menstrual cycles and reproduction to occur. Weight is not the only cause to consider, though. If a woman has never had menstrual bleeding, there may have been a problem with the normal development of the uterus or the vagina. If a woman had menstrual cycles previously, but then stopped, this could be due to a problem with the uterus itself, due to scar tissue inside the uterine cavity or premature menopause. If the uterus has not formed or if menopause has occurred, pregnancy is not possible.