Progesterone is one of the hormones that your body secretes each month as part of your normal reproductive cycle. The hormone helps prepare your body for pregnancy, and in the event of pregnancy, helps you maintain the pregnancy. Low progesterone can lead to miscarriage in certain cases, though some of these miscarriages are preventable.
Role of Progesterone
The role of progesterone is very similar whether or not you're pregnant -- it helps the uterine lining to thicken, and it helps to maintain the integrity of the uterine lining. During a normal menstrual cycle -- one in which you don't conceive -- your progesterone levels fall toward the end of your cycle, and you shed the uterine lining. If you do conceive, however, progesterone levels stay high, and you maintain the uterine lining.
Uterine Lining
The purpose of the uterine lining is to give a fertilized egg somewhere to implant. Your developing baby begins building the placenta within just a few weeks of fertilization, but the organ isn't complete until the third or fourth month of pregnancy. Until it is, the embryo depends entirely upon the lining of the uterus to supply it with oxygen and nutrients, explain Heidi Murkoff and Sharon Mazel in their book "What To Expect When You're Expecting."
Miscarriage
If your progesterone levels are too low, you can shed the lining of the uterus even if you've conceived a child. When this happens, you have a miscarriage, as the developing embryo leaves the uterus along with the uterine lining. Typically, you need progesterone levels of at least 15 ng/mL to maintain a healthy pregnancy, explains the Advanced Fertility Institute of Chicago. Levels lower than this can indicate that you may be at increased miscarriage risk.
Other Causes
Low progesterone doesn't necessarily indicate a threatened miscarriage; it can also indicate an ectopic pregnancy. The Advanced Fertility Institute of Chicago explains that in this kind of pregnancy -- also called a tubal pregnancy -- the developing egg implants outside the uterus and begins to develop, though it doesn't usually develop completely normally. Typically, ectopic pregnancies result in low hormone levels. They are not maintainable pregnancies, and must be terminated.
Treatment
Your doctor may check your progesterone levels early in pregnancy to assess whether you might have an ectopic pregnancy or be at risk for a miscarriage. If you show a normal uterine pregnancy but have low progesterone, your obstetrician may supplement you with pharmaceutical progesterone -- often in pill form -- for the first several months of your pregnancy. This will help you maintain the uterine lining and will help prevent miscarriage.
References
- "What to Expect When You're Expecting"; Heidi Murkoff and Sharon Mazel; 2008
- Advanced Fertility Center of Chicago: Progesterone Levels
