Progesterone is a hormone produced in the ovaries during the second half of the menstrual cycle. During pregnancy, it is produced in larger quantities by the placenta. At the end of the pregnancy, a drop in progesterone levels will help start labor.
Progesterone helps to build the lining of the uterus into which the fertilized egg will implant. Progesterone is also essential in passing into the developing baby’s circulation, where it is converted in the adrenal glands to corticosteroid hormones. A pregnant woman will have roughly 10 times more progesterone in their blood while pregnant as compared to when they are not pregnant. Progesterone levels rise gradually throughout the entire pregnancy. Abnormally high levels of progesterone may indicate you are having twins or more, or it may be a sign of a molar pregnancy. A progesterone test can help monitor the health of the placenta as well as the ovaries during pregnancy.
Low progesterone levels may be a physical sign of miscarriage during the first 12 weeks. It is most likely that the lack of progesterone does not cause the miscarriage, rather it is the body’s response to the inevitable loss of the pregnancy. Some practitioners may give progesterone to help prevent miscarriage, but this may well not be of any real help.
The following table is a guide to what the progesterone levels can be during pregnancy. Again, you can see the range of normal levels is very wide. Progesterone is measured in nanograms per milliliter (ng/ml).
Before pregnancy: 1 to 28 ng/ml
Conception to 12 weeks: 9 to 47 ng/ml
12 to 28 weeks: 17 to 146 ng/ml
28 weeks till birth: 55 to 200 ng/ml