Many of your body's hormones work together to help maintain your pregnancy. One of these hormones is called progesterone, which also has functions in the reproductive cycle of non-pregnant females. If your progesterone level is low during pregnancy, you can miscarry your baby. For this reason, physicians may test for progesterone early in pregnancy.
Progesterone and Reproduction
During your normal monthly reproductive cycle, progesterone serves the role of helping to proliferate the lining of the uterus. When you ovulate, leftover tissue in the ovary called the corpus luteum produces high levels of estrogen and progesterone. Your body responds to these hormones by thickening the lining of the uterus, in anticipation of implantation of a fertilized egg. If conception doesn't occur, the corpus luteum degrades after about 14 days, hormone levels fall, and you menstruate.
Fertilization
If conception occurs, the fertilized egg begins to secrete a hormone called hCG, or human chorionic gonadotropin. This hormone communicates with the corpus luteum, so that it doesn't degrade, but keeps producing hormones. The corpus luteum, in continuing to produce estrogen and progesterone, helps maintain the uterine lining. The fertilized egg implants in the uterine lining and begins to develop. If progesterone levels are low, or if they fall, you'll shed the lining of the uterus and lose the pregnancy.
Low Progesterone
According to the Advanced Fertility Center of Chicago, progesterone levels need to be above around 15 ng/mL for a pregnancy to be viable. If progesterone levels are lower, it can indicate a problem with the pregnancy. For instance, ectopic pregnancies -- those in which the fertilized egg implants outside the uterus -- often present with low progesterone. An ectopic pregnancy is not viable, and must be terminated.
Miscarriage Potential
Even an egg that implants properly can be threatened by low progesterone -- if a woman's progesterone is below 15 ng/mL, even if the egg has implanted in the uterus, she's at risk for a miscarriage. Physicians can treat low progesterone in the case of a correctly-implanted egg by supplementing with pharmaceutical progesterone, explain Heidi Murkoff and Sharon Mazel in their book "What To Expect When You're Expecting." This can help you maintain a pregnancy that you might otherwise lose.
Importance of Progesterone
Typically, the corpus luteum continues producing progesterone until around the third or fourth month of pregnancy, at which point the placenta has developed. The placenta then takes over progesterone production, and also takes over from the uterine lining the role of providing nutrients and oxygen to your growing baby. Generally, physicians no longer worry about low progesterone after the third or fourth month of pregnancy, because of placental development.
References
- Advanced Fertility Center of Chicago: Progesterone
- "What to Expect When You're Expecting"; Heidi Murkoff and Sharon Mazel; 2008
