Low Progesterone: What the Test Can and Cannot Show

Not as a standalone one, on current evidence. ASRM's 2021 committee opinion on luteal phase deficiency states that although progesterone matters for implantation and early embryonic development, luteal phase deficiency has not been proven to be an independent entity causing infertility or recurrent pregnancy loss. The same document says controversy remains over how to diagnose it and, assuming it can be diagnosed accurately, whether treating it improves outcomes.

What a low mid-luteal progesterone usually indicates is that ovulation did not happen, or did not happen when the blood was drawn. Progesterone comes from the corpus luteum, which only exists after an egg is released. So the useful question a low result raises is not 'how do I raise my progesterone' but 'did I ovulate, and if not, why not'.

ASRM also notes that an abnormally short luteal phase — ten days or fewer — is the clinical finding the label is associated with, and that it has been described in fertile, normally menstruating women too.

Because progesterone is released in pulses, so the figure you get depends heavily on the minute the needle went in. Fujimoto's 1990 study sampled 28 normal menstrual cycles daily, and in five women every 20 minutes across a 24-hour mid-luteal admission. It found pulsatile variation, and a significant circadian swing in seven of ten women — with the time of day of the peak differing between women, so there is no single 'best' hour to draw it.

The most telling result is what happened when the authors built reference ranges from randomly selected single daily values out of those same 28 normal cycles. Five ranges from one dataset of healthy women gave lower limits between 2.7 and 6.1 ng/mL and upper limits between 24.2 and 42.1 ng/mL. A 'normal range' that unstable cannot support a cut-off, which is why there is no agreed threshold defining low progesterone.

Add two more sources of drift: which cycle day counts as mid-luteal depends on when you actually ovulated, not on day 21, and different laboratories run different assays.

In assisted reproduction cycles, and that is a narrower claim than it sounds. In IVF and ICSI the drugs used to stimulate and then trigger the cycle disturb the body's own luteal phase, so progesterone is given to replace what the cycle no longer produces properly. The Cochrane review of luteal phase support in assisted reproduction pooled 94 randomised trials covering 26,198 women. Comparing progesterone against placebo or no treatment, it found a higher rate of live birth or ongoing pregnancy, odds ratio 1.77 (95% CI 1.09 to 2.86, from 5 trials and 642 women).

Read the grading alongside the result. The review rated that finding very low-quality evidence, and noted that most included studies had unclear or high risk of bias in most domains. So the honest summary is that luteal support is standard practice in ART, that the direction of effect favours it, and that the evidence underneath it is weak.

The point that matters for you: this evidence was generated in women whose luteal phase had been disrupted by fertility drugs. It does not transfer to a woman trying to conceive naturally, whose corpus luteum has not been interfered with. That read-across is the single most common error in writing about this hormone, and it is the reason progesterone is sold to people who have no reason to take it.

ESHRE's recurrent pregnancy loss guideline, updated in 2022, answers this in two parts, and both parts matter.

• For women with unexplained recurrent pregnancy loss, the guideline states that vaginal progesterone does not improve live birth rates. This is a conditional recommendation.
• For the narrower group of women with three or more pregnancy losses who then have vaginal bleeding in a subsequent pregnancy, it states that vaginal progesterone may improve live birth rate. Also a conditional recommendation.

So there is a specific, defined situation in which a guideline supports it, and outside that situation the same guideline says it does not improve live birth. 'Progesterone prevents miscarriage' is not what the guideline says, and a pregnancy loss is not evidence that your progesterone was low.

This is the part of the page worth reading twice, because most of what is sold in this area sits in the gap between these statements:

• It does not establish luteal phase deficiency as a cause of infertility or recurrent pregnancy loss. ASRM 2021 states it has not been proven to be an independent entity.
• It does not establish a threshold below which progesterone is 'low'. Five reference ranges from the same 28 normal cycles in Fujimoto 1990 disagreed on the lower limit by more than twofold.
• It does not establish that progesterone helps women trying to conceive naturally. The Cochrane evidence is from assisted reproduction cycles, where the drugs used have disturbed the luteal phase.
• It does not establish that supplementation corrects anovulation. If an egg was not released, adding progesterone does not release one; it can make a bleed look more regular while the underlying problem is untouched.
• It does not establish that any food, vitamin or herbal product raises progesterone or improves the chance of pregnancy. The claims commonly made for vitamin B6, zinc, magnesium and Vitex in this context are not supported by any source cited on this page, and we have not found trial evidence for a fertility outcome to put here.
• It does not establish that symptoms such as spotting, mood change or breast tenderness indicate low progesterone. These are common and non-specific, and no source below links them to a measured level.

If you have been told your progesterone is low and it has left you feeling that your body is failing at something basic, that is a very common reaction to this particular result, and the state of the evidence above is a better guide than the feeling.

No. Do not stop a prescribed progesterone on the strength of an article, and particularly not during a treatment cycle or a pregnancy. Your doctor knows things this page cannot: whether you are in an ART cycle, what your history of loss is, whether you are bleeding, and what else is on your chart.

What this page is for is making the next conversation sharper. Reasonable things to ask:

1. Which of the situations above am I in — an ART cycle, recurrent loss with bleeding, or something else?
2. What is this meant to change, and how will we know whether it worked?
3. When do we stop it?
4. Was my mid-luteal progesterone the reason for starting, and if so, is repeating it going to change the plan?

And the corollary: if nobody has prescribed it, progesterone is a prescription medicine and not a supplement to start on your own. If you are being sold it without a prescription and without one of the situations above applying, the evidence above is the reason to be sceptical.

A low mid-luteal progesterone is most useful as a signal to look at ovulation. The common findings behind absent or unreliable ovulation are polycystic ovary syndrome, thyroid disease, a raised prolactin, and low hypothalamic drive — each with its own treatment, none of which is progesterone.

There is also the timing possibility worth excluding first: a level drawn on a fixed day 21 in a cycle where ovulation happened late will be low simply because it was taken too early, not because anything is wrong.

• Understanding anovulation
• Progesterone supplements in fertility treatment
• Which hormone problem causes irregular periods
• What estrogen does across one menstrual cycle
• Luteinized unruptured follicles