Irregular or abnormal ovulation accounts for approximately 25 percent of all infertility cases. Ovulation normally occurs twelve to sixteen days before the onset of menstruation. During ovulation, progesterone is released. Progesterone is the hormone that transforms the uterine lining into a receptive environment for implantation and nurturing of the fertilized egg. If you feel you're not ovulating normally, there are several tests you can take to determine the regularity of ovulation. You may complete a basal body temperature chart by taking your temperature orally each morning for a month and recording it. The release of progesterone usually causes a .5 (point five) to one degree rise in temperature. You may also use an over-the-counter prediction kit that tests the urine. A physician may perform a pelvic ultrasound examination or a biopsy to evaluate your patterns of ovulation. If you're not ovulating, you may be prescribed medication to stimulate ovulation. Up to 80 percent of women taking ovulation drugs begin to ovulate regularly, and if no other factors need treatment, over half may become pregnant within the first six induced ovulations.