Early in your pregnancy, your progesterone levels should generally be on the increase. Progesterone is one of the female reproductive hormones with important roles both in your normal menstrual cycle and in pregnancy. Proper blood levels of progesterone help maintain your uterine lining, which in turn helps maintain your pregnancy.
Sources of Progesterone
Under normal circumstances -- that is, during the majority of your menstrual cycles -- the source of progesterone in your body is the corpus luteum. This is an area of tissue in your ovary that secretes both estrogen and progesterone, causing the lining of the uterus to thicken each month in preparation for implantation of a fertilized egg. Later in pregnancy -- after the third or fourth month -- your placenta becomes the most significant source of progesterone.
Normal Menstruation
During a normal monthly cycle, your uterine lining thickens as an egg matures in your ovary. Upon ovulation, the corpus luteum continues secreting estrogen and progesterone for around two weeks, maintaining the uterine lining. If you don't conceive, the corpus luteum eventually disintegrates and hormone levels fall. This causes sloughing of the uterine lining, or a menstrual period. This highlights the important role of progesterone in early pregnancy -- you need threshold levels of progesterone to maintain the uterine lining, and therefore maintain the pregnancy.
Low Progesterone
There are several concerns associated low progesterone early in pregnancy. According to the Advanced Fertility Center of Chicago, low progesterone is defined as any level less than 15 ng/mL. One concern is that you could have an ectopic, or tubal, pregnancy. These occur when a fertilized egg implants outside the uterus, and they are not sustainable pregnancies. While not all ectopic pregnancies present with low progesterone, many do. Another concern of low progesterone is that it will lead to spontaneous shedding of the uterine lining and loss of the pregnancy.
Luteal Phase Defect
Another potential cause of low progesterone is a luteal phase defect. MayoClinic.com notes that this occurs when the corpus luteum survives less than the typical 14 days, making it difficult for a fertilized egg to embed in the uterine lining. This leads to a pregnancy that occurs -- you will even get a positive result on a pregnancy test -- but doesn't last, because the zygote never embeds in the lining. If your obstetrician suspects a luteal phase defect, you may receive pharmaceutical or medically-administered progesterone, which generally comes in the form of either injections or pills.
Progesterone Testing
Unless you actually miscarry, there aren't any outward signs of low progesterone in early pregnancy. Many doctors will do a blood test during your first weeks of pregnancy, however, to determine your progesterone levels, explains Dr. Miriam Stoppard in her book "Conception, Pregnancy and Birth." If the doctor finds that you appear to be having an otherwise normal pregnancy with low progesterone levels, it's possible to supplement progesterone through the first few weeks or months of your pregnancy to help you maintain it.
References
- Advanced Fertility Center of Chicago: Progesterone
- MayoClinic.com: Luteal Defect
- "Conception, Pregnancy and Birth"; Miriam Stoppard, M.D.; 2008
