What Happens if my Progesterone Levels are too low?
By Dr. Kate Dudek
Low progesterone levels can be a marker of anovulation. Under normal conditions, progesterone levels rise during the luteal phase of the menstrual cycle. The luteal phase of the cycle follows ovulation and is always the 10-14 days before menstruation starts, regardless of ‘normal’ cycle length. Without ovulation, the levels of progesterone do not increase. Thus, checking progesterone levels is one way of assessing whether or not you are ovulating (measuring basal body temperature is another way, as this will rise 0.5°C after ovulation). If blood serum progesterone levels do not get above 1.8ng/ml then ovulation has not occurred. An optimal reading is 8ng/ml progesterone midway through the luteal phase. This is 5-7 days before you get your period and is the point at which levels of this hormone are at their highest.
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, there is no progesterone. It is essential to wait until after ovulation (or the time at which ovulation should have occurred) to check levels. 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, it is normal to no longer produce progesterone. 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 look into reasons why your body is not ovulating. 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 hypothalmic 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 are constant and sustained, PCOS is something that should be considered. Identifying and rectifying the cause of your anovulation should ensure that progesterone levels return to normal.