Progesterone is a female hormone that plays a critical role in preparing your body for conception. With low levels of progesterone, it is difficult for your body to either conceive a child or carry the child to term. This significantly impacts fertility -- as such, physicians will sometimes look for progesterone deficiencies if a woman is having trouble conceiving or carrying a baby.
Progesterone and Menses
In the normal menstrual cycle, progesterone levels start off quite low. As an egg begins to mature in your ovary, the tissue surrounding the egg begins to produce the hormone progesterone, which causes the lining of your uterus to thicken. After ovulation, this tissue -- now called the corpus luteum -- continues to produce progesterone in relatively large quantities for many days. This helps maintain the uterine lining so that if fertilization occurs, there will be a place for the fertilized egg to implant.
Progesterone and Pregnancy
You need progesterone not simply to prepare the uterus for implantation of a fertilized egg, but for maintenance of the early pregnancy as well. Before a developing baby forms in the placenta -- an event typically accomplished by the end of the third or fourth month of pregnancy -- it's entirely dependent upon the uterine lining for nutrients and oxygen supply. Since progesterone maintains the uterine lining, low progesterone can cause sloughing of this lining and loss of pregnancy.
Luteal Phase Defect
One way in which low progesterone can contribute to infertility is through what's called a luteal phase defect, explains MayoClinic.com. A luteal phase defect occurs when the luteal phase -- the time during which the corpus luteum secretes progesterone to prepare and thicken the uterine lining -- is abnormally short. This results in malformation or insufficient formation of the uterine lining, and even if fertilization occurs, there's no place for a fertilized egg to implant.
Early Miscarriage
It's also possible to have a normal luteal phase and conceive normally, and yet be unable to carry an embryo beyond the first few weeks due to a progesterone deficiency. The Advanced Fertility Center of Chicago explains that progesterone levels lower than 15 ng/mL can lead to spontaneous shedding of the uterine lining, which leads to loss of the pregnancy. If you test positive for pregnancy and then have a period shortly thereafter on repeated occasions, your doctor may check your progesterone levels.
Treatment
Physicians can use progesterone administered in injected or oral form to help relieve low progesterone-related infertility, explains AmericanPregnancy.org. Sometimes, this therapy occurs in combination with other infertility treatments, depending upon the likely cause of infertility. If it appears, however, that a woman can conceive naturally and simply has difficulty maintaining the pregnancy due to low progesterone, typically progesterone is the only indicated therapy.
