Low level of progesterone refers to serum progesterone concentration below the lower limit of the reference range (Pic. 1) for a given age group and, in fertile women, for the specific phase of the ovarian cycle (Pic. 2). Progesterone is naturally low in prepubescent girls and in postmenopausal women. In fertile women, its concentration varies greatly depending on the phase of ovarian cycle. After the woman ovulates, the newly formed corpus luteum starts producing large quantities of progesterone, and the serum progesterone concentration almost doubles. This induces the effects that are typical for the luteal phase of the ovarian cycle. If the serum progesterone is low during the luteal phase, the phase itself is shorter than usual, or both, the condition is called luteal phase defect.
The main physiological roles of progesterone are as follows:
When the corpus luteum fails to produce sufficient amount of progesterone, the endometrium doesn’t undergo the secretory changes in the secretory phase, and is not capable of supporting the implantation of an embryo. This in turn results in infertility or in recurrent pregnancy loss.
Progesterone is essential for the luteal phase of the menstrual cycle, for the implantation of an embryo and for the function of the uterus during pregnancy. Low progesterone causes distrubances in these processes and may lead to severely impaired fertility.
In nonpregnant women, low levels of progesterone may lead to irregular or absent periods and abnormal uterine bleeding. They may also experience mood swings, depression and low sex drive. Progesterone is necessary for the changes of the endometrium during the luteal phase, including the thickening of the endometrium and growth and activity of the endometrial glands. These changes are necessary for the succesful implantation of the fertilized egg, and therefore for the initial stage of pregnancy. Without these changes in the endometrium, the fertilized egg will not be able to implant, and pregnancy will not occur.
Because progesterone is produced by the ovary (more specifically, by corpus luteum, which is contained within the ovary), its levels can be low in various conditions of hypogonadism (decreased secretion of sex hormones by the gonad). In hypogonadism, the levels of estrogen are usually low as well. Hypogonadism has many causes, both congenital and acquired. Women suffering from hypogonadism are infertile, or have significantly reduced fertility.
Low progesterone can also cause miscarriage in pregnancy. Initially, progesterone produced by the corpus luteum is necessary for maintaining the function of uterus. After 8-10 weeks of pregnancy, the progesterone production is largely taken over by the placenta. Low progesterone production by the corpus luteum can cause an unviable pregnancy and death of the embryo. If symptoms of low progesterone are present, the patient should undergo blood test for the level of progesterone and a gynaecologic examination.
Low level of progesterone may lead to many different problems, including lower fertility and various symptoms affecting the quality of life. However, there are several types of treatment that women with low progesterone may benefit from. The administration of hormones, called hormone therapy, utilizes administration of exogenous progesterone in various forms. This treatment may be the sustainable solution for perimenopausal (approaching menopause or shortly after menopause) and postmenopausal women.
Several hormones including progesterone may be also administered to support the function of the corpus luteum and increase the chance of implantation. This is termed luteal support, and it may increase the pregnancy rate and live birth rate in women undergoing IVF (in vitro fertilization) procedure.