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.