FSH is the abbreviated name for follicle stimulating hormone. It is made in the pituitary gland and its secretion is controlled by part of the brain called the hypothalamus. FSH causes growth of ovarian follicles and causes the follicles to secrete estrogens. The hypothalamus responds to signals from the ovaries as a guide to its stimulation of the pituitary gland to secrete FSH. The concentration of FSH changes throughout the menstrual cycle. The diagram below shows approximate levels of the 2 pituitary hormones which stimulate the ovaries. On cycle day 3, FSH is at its lowest level during the cycle. If blood is drawn too close to the time of ovulation, the FSH level will be higher, and may provide misleading information.
It is also important to note that there are several companies providing “kits” to measure FSH. Different labs may use different “kits” and the same sample may provide slightly different results. It is important to know what the standards for the lab are in order to interpret the results.
An ovarian follicle consists of an egg and a surrounding cluster of cells called granulose cells. All the eggs a woman will ever have were placed in her ovaries when she was a very early pregnancy in her mother’s uterus. Soon after that initial installation of these very immature eggs, eggs start to die off and no more eggs replace those which are lost. The estimate is that about 90% of the original egg number is lost by the time a woman is born, and the attrition continues the rest of her life, until she runs out of eggs.
The granulose cells surrounding the eggs have several functions. One is to help maintain the eggs in a sort of suspended animation until it is time to continue egg maturation. During each month, several eggs start to mature, but typically only one is released in the process of ovulation. The remainder of the eggs undergoing the maturation process die.
Another function of granulose cells is to secrete hormones. During the early part of the menstrual cycle, granulose cells secrete estrogens. After ovulation, they also secrete progesterone. There is another pair of hormones secreted by granulose cells. They are called inhibins. In addition to the weak inhibition of FSH by estrogens, inhibins strongly inhibit FSH secretion by the pituitary gland. As a woman runs out of eggs, she also runs out of granulose cells and her production of both estrogens and inhibins declines. As circulating levels of inhibins falls, FSH secretion rises. Therefore, high FSH levels imply that a woman is either running out of eggs, or she no longer has available eggs. Fortunately, today, we can offer a woman who no longer has useable eggs the services of an egg donor to help achieve a pregnancy.
Dr. Jacobs is a Reproductive Endocrinologist, practicing in Carrollton, Texas, a northern suburb of Dallas. He completed his residency training in obstetrics and gynecology at Baylor College of Medicine in Houston, and remained at that institution to become its first fellow once Baylor achieved accreditation for an advanced training program in Reproductive Endocrinology and Infertility. Dr. Jacobs has served on the faculty of several medical schools and was director of Reproductive Endocrinology at Texas Tech Health Science Center in Amarillo. Currently, in addition to his clinical activities caring for infertile patients and those with recurrent pregnancy loss, he is Chairman of the IVF committee at Baylor Medical Center in Carrollton.
Barry Jacobs, M.D., 4323 M. Josey Lane, Suite #201, Carrollton, TX 75010 www.texasfertility.com Phone: 972-394-9590 Fax: 972-394-9597