A progesterone test measures the level of progesterone in the blood. Progesterone is a hormone made by a woman's ovaries. Progesterone plays an important role in pregnancy. It helps make your uterus ready to support a fertilized egg. Progesterone also helps prepare your breasts for making milk. Progesterone levels vary during a woman's menstrual cycle. The levels start out low and then increase after the ovaries release an egg. If you become pregnant, progesterone levels will continue to rise as your body gets ready to support a developing baby. If you do not become pregnant (your egg is not fertilized), your progesterone levels will go down and your period will begin. Progesterone levels in a pregnant woman are about 10 times higher than they are in a woman who is not pregnant. Men also make progesterone but in much smaller amounts. In men, progesterone is made by the adrenal glands and testes. Other names: serum progesterone, progesterone blood test, PGSN.