How Does Progesterone Work?

Progesterone plays a large role in the female fertility cycle. Lowered progesterone levels may cause infertility, miscarriage and premenstrual syndrome (PMS) symptoms. Understanding how progesterone works in the body and how to increase levels when needed may help alleviate common reproductive problems.

The Fertility Cycle

The average woman's 28-day fertility cycle can be divided into three phases. The first two consist of menstruation and ovulation, but progesterone plays an important role in the last phase, also called the luteal phase. After ovulation, the follicle that released the egg turns yellow and is now called a corpus luteum. The corpus luteum secretes progesterone, a basic female hormone. Progesterone has several effects on the woman's fertility cycle.

Progesterone's Effects

For the 10 to 14 days immediately after ovulation, elevated progesterone levels make sure the lining of the uterus maintains its rich, thick blood supply to nourish a fertilized egg. Progesterone suppresses subsequent ovulation during the luteal phases. A woman's resting body temperature--her basal body temperature--remains elevated by about 0.4 degrees because of the surge of progesterone. In addition, during this time cervical mucus thickens and forms a plug in the cervical canal and the cervix lowers. All of this is to prepare the body for a possible implantation and pregnancy immediately after ovulation.

Progesterone and Fertility Problems

When a woman has low progesterone, she may have shortened luteal phases. This can be especially troubling for a woman trying to conceive, as this lack of progesterone prevents an egg from implanting in the uterus before the cervical lining is shed in the form of monthly menstruation. Low progesterone may also cause premenstrual syndrome (PMS) and a general uncomfortable feeling during the luteal phase. Also, women who have lowered levels of progesterone may experience miscarriages, as their bodies aren't making enough to maintain a pregnancy.


To combat low progesterone levels, Marilyn Shannon, author of "Fertility, Cycles and Nutrition," recommends taking 200-800 milligrams of vitamin B6 daily 2. Vitamin B6 may lengthen the luteal phase, thus allowing a fertilized egg to implant. The raised progesterone levels this supplement provides will also bring relief for those suffering with PMS.

Other Treatments

Synthetic treatments for elevating progesterone levels also exist. Provera--synthetic progesterone--may be prescribed for prolonged menstrual bleeding due to a hormonal imbalance. Birth-control pills may also be effective. In addition, progesterone creams may be beneficial for keeping the rich cervical lining intact during the fertility cycle. Menopausal women may find relief from these creams, as progesterone levels decline as a woman ages.