I have been having poor ovulations or lack of ovulations since my miscarriage almost two years ago. Since then, I have had very few cycles (three in a year). I charted my temperatures, and my doctor said that I am not ovulating. He said there is a pituitary problem, and he prescribed Provera to start up my period. What exactly does the Provera do to induce my period?

K.E.

It is not unusual to have a change in your menstrual cycles after a miscarriage. Normally, during the first half of your menstrual cycle, the ovarian follicle -- the pocket on the ovary in which the egg grows -- produces estrogen, which causes the uterine lining to thicken. Once you ovulate, the follicle begins producing progesterone to stabilize the uterine lining's growth and prepare it for implantation of the fertilized egg. If pregnancy does not occur, the ovary stops making progesterone, and the level drops. It is the drop of progesterone that brings on the menstrual period, in which the uterine lining is shed.

Provera is synthetic form of progesterone produced from chemical modification of male hormones. If your uterine lining has been stimulated by estrogen, and you then take Provera, changes occur that trigger a menstrual period when the Provera is stopped. So bleeding after Provera indicates that you make enough estrogen to stimulate growth of the uterine lining, that the cervix and uterine lining are structurally normal, and that you are not pregnant (although we prefer not to give Provera to women who may be pregnant, to avoid possible harm to the fetus).

Still, the short course of Provera only works to bring on bleeding. It does nothing to address your ovulation problem or any underlying conditions that might be associated with a lack of ovulation. Provera does nothing to evaluate or treat a possible pituitary problem.

An in-depth review of your medical history, a physical examination, and a transvaginal ultrasound examination are necessary first steps in evaluating your problem. If you have gained weight or have abnormal hair growth, I would also measure male hormones and fasting insulin levels. Blood tests for the hormones TSH and prolactin can help determine if a pituitary or endocrine malfunction is behind your ovulation problem. Only after this information is available can your physician work with you to develop a plan to help restore regular, ovulatory menstrual cycles.