What is a Normal Progesterone Level?
Progesterone is a steroid hormone initially secreted after ovulation by the corpus luteum, an area in the ovary which develops after ovulation. Progesterone prepares the endometrium, the lining of the uterus, for implantation and a possible pregnancy. It prevents contractions of the uterus and the development of a new follicle, and during pregnancy, it is produced by the placenta and maintains the pregnancy until birth. Prior to ovulation, progesterone levels are very low. They increase right after ovulation and reach levels above 10 ng/ml usually by 5-7 days after ovulation takes place. If you are not pregnant, progesterone levels usually decrease around the time of the next menstrual period bleeding. Before ovulation, progesterone is well below 10ng/ml and after ovulation, it is well above 10ng/ml. The time right after ovulation until the next menstrual period is called the “corpus luteum phase” or the “luteal phase.”
During the luteal phase, the fertilized egg travels through the fallopian tube into the uterus where it implants usually 6-12 days after fertilization. The normal luteal phase lasts on average 14 days, and it can be anywhere from 12 to 17 days long. Progesterone levels normally rise during the first 36-38 weeks of the pregnancy, then fall towards the due date. Pregnancy cannot be diagnosed by testing progesterone levels. Only the presence of hCG the pregnancy hormone hCG diagnoses a pregnancy. Progesterone levels are only averages and they can change based on many variables. For example, the timing of the cycle, whether you ovulate or not, which lab tested them, whether blood is taken after you eat or before, and whether it's in the morning or afternoon, can all affect the outcome of a progesterone level test.