Progesterone is one of the hormones that your body depends upon to help maintain pregnancy. If you experience a miscarriage, your doctor will likely test for a variety of potential causes, some of which have to do with production of progesterone and your progesterone levels during the early weeks of pregnancy.
Role of Progesterone
The role of progesterone in pregnancy is quite similar to its role when you're not pregnant -- progesterone helps to thicken the uterine lining and maintain it, preventing sloughing and menstruation. In preparation for fertilization of an egg each month, your progesterone levels rise, causing the uterine lining to thicken. A fertilized egg then implants in the thickened uterine lining. In the absence of progesterone, you slough the uterine lining and menstruate.
Early Pregnancy
An important distinction between early pregnancy and the end of a normal monthly reproductive cycle is that if you're pregnant, you must maintain the uterine lining. Progesterone comes from tissue in your ovary called the corpus luteum, which normally disintegrates about 14 days after ovulation, causing progesterone levels to fall. A fertilized egg signals the corpus luteum to continue producing hormones, which maintains the uterine lining.
Miscarriage
If you have low progesterone in the early days of pregnancy, you can slough your uterine lining. This causes loss of the pregnancy, or spontaneous miscarriage, because the embryo is completely dependent upon the uterine lining until the third or fourth month of pregnancy, at which point the placenta has finished developing. The Advanced Fertility Center of Chicago notes that, in a normal pregnancy, progesterone levels should be greater than 15 ng/mL.
Low Progesterone
You could have low progesterone for several reasons early in pregnancy, making you susceptible to early miscarriage. In some cases, the fertilized egg implants outside the uterus, in what's called an ectopic or tubal pregnancy. These pregnancies aren't viable but do present with low progesterone. They either self-terminate or are terminated by a physician. Alternately you could have a luteal phase defect, in which the corpus luteum doesn't secrete progesterone long enough for an egg to implant. Finally, you could simply be producing limited progesterone for undetermined reasons.
Solution
If your physician determines that you have low progesterone early in pregnancy but that the pregnancy is otherwise viable, the doctor will likely suggest progesterone supplements. These, which you generally take either in pill form or as an injection, help to maintain your uterine lining through the early weeks and months of pregnancy, until such time as your body increases its progesterone production, or the placenta has finished forming. The placenta also secretes progesterone, typically eliminating the need for supplements.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- Advanced Fertility Center of Chicago: Progesterone Levels
