Is Low Progesterone Affecting Your Fertility? Signs, Testing & Root Causes

The menstrual cycle is defined primarily by two phases; the follicular phase and the luteal phase. Each phase has certain hormones associated with it - and if you’ve ever looked at a diagram of the cycle you’ve probably seen the ups and downs of four different hormones: estrogen, follicle stimulating hormone (FSH), luteininzing hormone (LH), and progesterone. 

Estrogen, FSH and LH are all key players in the follicular phase of the cycle: FSH drives egg development, estrogen nourishes egg growth and LH surges to help release it for ovulation.  

Progesterone is the primary hormone in the luteal phase; it is produced by the corpus luteum of the ovulated egg and is essential for a healthy pregnancy to develop. 

Why is it so important?

Progesterone is responsible for developing the uterine lining, or the endometrium.  The endometrium needs to be a certain thickness to be strong enough for an embryo to implant.  It’s what nourishes the embryo and helps it stay long enough for the placenta to develop and take over. 

How do I know if I have low progesterone?

The two most notable signs would be if you have short cycles (think less than 25 days, definitely if around 21 days) or if you experience spotting before your period.  Other symptoms that may indicate low progesterone levels include

• periods with light bleeding

• short periods

• PMS symptoms that start shortly after ovulation instead of closer to your period

• luteal phase of 10 days or less (if you track ovulation)

• recurrent pregnancy loss. 

A more concrete way to know would be to get your serum progesterone tested around day 21-23 of your cycle (or 7 days after ovulation).  Timing matters for serum testing because progesterone peaks about 7 days after ovulation, so that gives the best indication of how high your progesterone is going to go for that cycle.  

Ideal serum (or blood) levels of progesterone to sustain pregnancy are 10-15ng/mL, though closer to 15ng/mL is optimal. That isn’t to say pregnancy cannot occur if your levels are less than 10ng/mL, but the risk of miscarriage increases significantly the lower the levels. If they are <3ng/mL, that is an indication that you have not ovulated.

I generally prefer serum testing over urine metabolite data that you may collect with trackers such as Inito or Mira, purely because the majority of research that has set treatment standards is based on serum testing.  That isn’t to say that urine metabolite testing can’t give valuable information on patterns and prompt further investigation, it’s just not typically what I rely on.  

What causes low progesterone?

Anovulation, or not ovulating, is one of the main causes of low progesterone in a cycle.  If you don’t ovulate, your body won’t actually produce progesterone during that cycle.  

Some of the clearer causes of this include PCOS, excessive exercise and nutritional deficiencies, chronic stress - essentially anything that may cause you not to have a period.  Underlying causes may include components such as thyroid, hypothalamic, or adrenal dysfunction or other things that may disrupt healthy estrogen production.

If you are going through IVF, low progesterone is a common issue due to the medications that are used. They have the effect of “switching off” your normal hormone flow in order to keep up with the specific timing required, as a result the corpus luteum can struggle to produce enough progesterone. 

Is low progesterone the same as a luteal phase defect?

It can be, but having low progesterone doesn’t automatically mean you have a luteal phase defect. 

A luteal phase defect, sometimes called luteal phase deficiency is a clinical diagnosis based on having a luteal phase that is less than 10 days, which is typically due to inadequate progesterone being produced by the corpus luteum.  However, you can have 11-14 day luteal phases and still have lower than optimal progesterone. 

Is there any way to improve my progesterone?

Yes, absolutely.  

Depending on what the cause is, there are several supplements and herbs (vitex agnus-castus is a frequent one) I commonly use in my practice to help balance out women' s cycles. We also address lifestyle and nutrition factors to ensure that we are supporting the whole hormonal process - from the brain to the ovaries. 

Sometimes, particularly if you are utilizing IVF, direct progesterone supplementation will be prescribed - typically as a vaginal suppository, but occasionally as an oral pill.

Low progesterone is one of the more common and correctable pieces of the fertility puzzle, but it does need to be identified first. 

If any of this feels familiar, that's worth paying attention to. 

I work with women navigating exactly these kinds of hormonal imbalances  - feel free to reach out or book a consult if you'd like to dig deeper.