Progesterone levels during the menstrual cycle
The menstrual cycle is split into the follicular phase and the luteal phase. The follicular phase is from day one of menstruation until ovulation, which is triggered by a surge in levels of luteinising hormone (LH). The luteal phase of the cycle follows ovulation and is always the 10-14 days before the next monthly period starts, regardless of ‘normal’ cycle length. Progesterone levels change during the cycle:
- Follicular phase – less than 1.5ng/mL.
- Ovulation – levels start to rise and peak after 6-8 days.
- Luteal phase – levels reach 7-10ng/mL.
Without ovulation, the levels of progesterone do not increase. Thus, checking progesterone levels midway through the luteal phase (usually day 21 or 22 of the cycle) is one way of assessing whether or not ovulation has occurred. If fertility status is being assessed progesterone levels will often be measured alongside Basal Body Temperature (BBT). BBT should rise by 0.5°C after ovulation.
If blood serum progesterone levels do not get above 3-4ng/mL during the luteal phase of the cycle, then it is highly unlikely that ovulation has occurred. If timed correctly to coincide with the midpoint of the luteal phase, levels of progesterone can reach 10ng/mL; this will be 5-7 days before you get your period and is the point at which levels of this hormone are at their highest.
What does it mean if your progesterone levels are low?
If progesterone levels are low there are a few factors to consider. Firstly, at what stage in the cycle were they checked? During the follicular phase, which comes before ovulation, progesterone levels will be very low, usually below 1.5ng/mL. If you want to check that ovulation has occurred you need to wait until the second half of the cycle, when a rise in progesterone is a good indicator of ovulation.
If you are on most forms of hormonal birth control, including the combined oral contraceptive pill, endogenous progesterone is suppressed, so levels will be low.
If you are postmenopausal, you will no longer be ovulating and as a result you will no longer experience a mid-luteal peak in progesterone levels. Serum progesterone levels will be very low, often less than 0.5ng/mL.
Finally, progesterone levels are inherently variable. They can fluctuate dramatically in a 90 minute time period, so it might just be a matter of repeating the test at a different time.
If, after taking all of these points into consideration, levels of progesterone are still low, you will need to consider that ovulation may not be happening and look into reasons why. The occasional anovulatory cycle is normal; it might happen when you have only just started your periods, or if you are recovering from a medical problem, such as hypothalamic amenorrhoea, or have just come off the pill. In these instances wait a few months and see whether your cycles become regular over time. However, if the lack of ovulation and low progesterone levels are constant and sustained, PCOS is something that should be considered.
In many cases, implementing lifestyle changes, such as losing weight, can help to rectify the symptoms of the condition, restore ovulation and ensure progesterone levels rise and fall as they should throughout the menstrual cycle. If this does not work, your doctor may recommend that you use medication to induce ovulation, for example, clomiphene citrate. These medications do not work for all women; so, following treatment, progesterone levels will be monitored to discern whether or not ovulation has occurred. Progesterone levels of 15ng/mL or higher indicate successful ovulation induction.
- Azziz, Ricardo, et al. “The Androgen Excess and PCOS Society Criteria for the Polycystic Ovary Syndrome: the Complete Task Force Report.” Fertility and Sterility, vol. 91, no. 2, Feb. 2009, pp. 456–488., doi:10.1016/j.fertnstert.2008.06.035.
- Holesh JE, Hazhirkarzar B, Lord M. Physiology, Ovulation. [Updated 2019 Oct 19]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441996/.
- Strauss, Jerome F., and Robert L. Barbieri. Yen & Jaffes Reproductive Endocrinology: Physiology, Pathophysiology, and Clinical Management. 7th ed., Elsevier, 2014.