To understand what progesterone levels during the first trimester of pregnancy mean, it is important to understand exactly what progesterone is, where it comes from, and what its function is during the first trimester, as well as during the rest of your pregnancy. In many cases, your health care provider may wish to check your progesterone levels during the first trimester, particularly during the first half of your first trimester. If your progesterone levels are too low during the first trimester, your health care provider may want to do more testing, and may take certain precautions to help you avoid a miscarriage.
Progesterone is produced in the ovaries. Specifically, something called the corpus luteum produces the progesterone. Later on, the placenta will take over the role of trying to maintain the progesterone levels during the first trimester. Progesterone has a specific role to play in the pregnancy process. Progesterone helps to prepare the lining of the uterus for the implantation of a fertilized egg, for example. Progesterone helps to provide a lining in the uterus that is rich in nutrients for your baby. Progesterone also helps to create the mucus plug during pregnancy. Progesterone even plays a role in helping to raise the basal body temperature after you ovulate.
During the first trimester, progesterone levels will rise. They will be at approximately 1 to 1.5 ng/ml during the first two weeks of the first trimester, right after conception. During weeks 2 through 4 of the first trimester, the levels of progesterone will rise to somewhere between 2 and 28 ng/ml. Progesterone levels will continue to rise during the first trimester, reaching a level somewhere between 9 and 47 ng/ml by the end of the first trimester. During the second trimester, progesterone levels will be in the 17 to 147 ng/ml range, and they will be between 55 and 200 ng/ml during the third trimester of pregnancy.
Low levels of progesterone during the first trimester can indicate that there is a threatened miscarriage. If you are concerned about your progesterone levels during the first trimester, you should speak with your health care provider.