Progesterone measurements are often used to determine if ovulation has occurred. The ovaries produce very small amounts of progesterone until ovulation happens. During the first half of the menstrual cycle (the follicular phase), progesterone levels are low – generally less than 3 ng/mL. Once ovulation occurs, the ovary starts producing progesterone in higher quantities and the blood progesterone level rises to above 3 ng/mL.
To document ovulation, the progesterone level can be tested any time during the second half of the menstrual cycle (the luteal phase). Traditionally, progesterone is tested about a week after ovulation occurs. If your cycle is 28 days long, the progesterone level should be tested around day 21. If you have a 35 day cycle, the progesterone level should be tested on day 28.
Interpretation of the progesterone level
Blood progesterone levels are often misinterpreted. Some physicians mistakenly believe that a progesterone level should be 10-12 ng/ml or higher to prove that a patient is ovulating or “ovulating well.” The truth is that progesterone levels vary greatly from hour to hour during the luteal phase and even at the peak (one week after ovulation). If you get your blood progesterone level tested a few times in the same day, the result will be different each time. There are some elegant studies showing that progesterone levels can be quite variable – from as low as 4 ng/ml to as high as 40 ng/ml in the same day! So a level of 6 ng/mL is not necessarily bad and a level of 30 ng/mL does not prove it is high enough long enough to allow for implantation.
Low progesterone levels (less than 3 ng/mL) can be seen any time before ovulation, immediately after ovulation, and just before menses begins, as serum progesterone levels rise and fall in a relatively symmetric fashion starting with ovulation and ending with menses. Therefore the day that blood was taken needs to be taken into consideration when evaluating the result. Also, a low progesterone level during the luteal phase could be due to a brief reduction in progesterone production.
Our physicians at Texas Fertility Center – San Antonio are ready to help you understand your cycle and make recommendations for you to help optimize your chances at building a family.
Make an appointment with Texas Fertility Center San Antonio to learn more about progesterone and to have a full fertility evaluation!