Progesterone

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What is progesterone?
Where is progesterone produced?
Function of progesterone
Progesterone across the menstrual cycle
Normal progesterone levels
Causes of low progesterone
Causes of high progesterone
Progesterone and fertility
When and how to test progesterone
Progesterone in traditional Chinese medicine
Acupuncture and progesterone
Chinese herbal medicine and progesterone
Diet, supplements and lifestyle
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1. What is progesterone?

Progesterone (P4) is a steroid hormone produced primarily by the corpus luteum after ovulation, and by the placenta during pregnancy. Its name reflects its primary role — pro-gestation, supporting and maintaining pregnancy. Progesterone is essential for transforming the uterine lining into a receptive environment for implantation, and for sustaining pregnancy through the early weeks until the placenta takes over.

Progesterone is one of a group of hormones called progestins. The other progestins (such as 17-hydroxyprogesterone) are mainly intermediates in the production of progesterone, cortisol and other steroid hormones.

Reference ranges vary from country to country and between laboratories. Always interpret your own result against the reference range provided by the laboratory that performed your test.

2. Where is progesterone produced?

The main sources of progesterone are:

Corpus luteum — the empty follicle sac after ovulation. Produces the bulk of progesterone in the second half of the menstrual cycle.
Placenta — takes over progesterone production from around 8–12 weeks of pregnancy.
Adrenal glands — produce small amounts year-round.
Ovaries (small amounts) — outside the corpus luteum.

3. Function of progesterone

The main functions of progesterone are:

Transforming the proliferative uterine lining into a receptive secretory lining ready for implantation.
Maintaining the uterine lining and preventing menstruation if pregnancy occurs.
Helping propel the egg along the fallopian tube.
Preparing the breast tissue for lactation.
Supporting early pregnancy until the placenta takes over.
Inducing T-helper 2 (TH2) cell production, which protects the implanting embryo from the maternal immune system.
Slowing GnRH pulse frequency, preventing further follicle development during the luteal phase or pregnancy.
Calming and slightly sedating effects on the brain — many women find their mood is more settled in the luteal phase as a result.

4. Progesterone across the menstrual cycle

Follicular phase (days 1–14): very low — typically <1 nmol/L.
Ovulation: rises in the 24 hours before and after ovulation as the corpus luteum forms.
Mid-luteal phase (day 21 in a 28-day cycle): peak — should be >30 nmol/L (9.4 ng/mL) to confirm ovulation.
Late luteal phase: falls if no pregnancy, triggering menstruation.
Pregnancy: rises progressively, reaching >500 nmol/L by the third trimester.

5. Normal progesterone levels

Typical reference ranges are:

Follicular phase: <1 nmol/L (0.31 ng/mL).
Mid-luteal phase (day 21): >30 nmol/L (9.4 ng/mL) confirms ovulation.
Pregnancy first trimester: 35–141 nmol/L.
Pregnancy third trimester: 200–700+ nmol/L.

Reference ranges vary from country to country and between laboratories.

6. Causes of low progesterone

Low progesterone in the luteal phase causes luteal phase defect, a frequently underdiagnosed cause of infertility and recurrent miscarriage. Causes include:

Inadequate corpus luteum function — often due to a poor LH surge or weak ovulation.
Hypothyroidism — low T3 reduces the conversion of pregnenolone to progesterone.
Stress and elevated cortisol — pregnenolone (the precursor to both cortisol and progesterone) is preferentially shunted to cortisol production under chronic stress (the so-called "pregnenolone steal").
PCOS — irregular or absent ovulation.
Premature ovarian failure.
Hyperprolactinaemia.
Early pregnancy loss — failing pregnancy with falling progesterone.

7. Causes of high progesterone

High progesterone is normal in:

The luteal phase — particularly mid-luteal.
Pregnancy.

It can also be raised in some forms of congenital adrenal hyperplasia and in some ovarian cysts.

8. Progesterone and fertility

Adequate progesterone is essential for:

Successful implantation — the lining must be progesterone-converted to be receptive.
Maintaining early pregnancy until the placenta takes over.
Preventing miscarriage in women with low progesterone.
Allowing the immune system to tolerate the embryo through TH2 dominance.

9. When and how to test progesterone

Progesterone is measured to confirm ovulation. The test should be performed seven days before the expected next period (rather than rigidly on day 21, which only applies to a 28-day cycle). A level above 30 nmol/L (9.4 ng/mL) confirms ovulation.

Progesterone is released in pulses, so a single low result should be interpreted with caution and ideally retested. Reference ranges vary from country to country. Always interpret your own result against the laboratory's reference range and discuss it with your doctor.

10. Progesterone in traditional Chinese medicine

In traditional Chinese medicine, progesterone most closely corresponds to Kidney Yang — the warming, activating, sustaining aspect of Kidney function that should rise progressively through the luteal phase. Low progesterone is most commonly seen as Kidney Yang deficiency, often combined with Spleen Qi deficiency. Symptoms typically include cold hands and feet, lower back ache, fatigue, scanty late periods and a tendency to early miscarriage.

11. Acupuncture and progesterone

Acupuncture has been shown to support corpus luteum function and progesterone production through its effects on the hypothalamic-pituitary-ovarian axis and on ovarian blood flow. By regulating the LH surge that triggers ovulation, acupuncture also supports the formation of a strong corpus luteum that can produce adequate progesterone. Treatment is most effective when given throughout the cycle, with particular focus on the days around ovulation and into the luteal phase.

12. Chinese herbal medicine and progesterone

Chinese herbal medicine takes a cycle-phase approach — different formulae for the follicular and luteal phases. Luteal-phase formulae warm and tonify Kidney Yang and support the corpus luteum. Common herbs include Tu Si Zi (Cuscuta), Ba Ji Tian (Morinda), Xu Duan (Dipsacus) and Du Zhong (Eucommia). Classical formulae include You Gui Wan and Wen Jing Tang.

13. Diet, supplements and lifestyle

To support healthy progesterone production:

Eat foods containing apigenin in the luteal phase — chamomile tea, celery, parsley, oregano. Apigenin has been shown to increase progesterone.
Avoid foods that block progesterone in the luteal phase — citrus fruits (hesperetin), large amounts of green vegetables (chlorophylline), excess vitamin E.
Ensure adequate vitamin B6, magnesium and zinc — all support corpus luteum function.
Vitex agnus castus (chasteberry) has been shown to improve progesterone.
Reduce psychological stress.
Avoid NSAIDs (diclofenac, naproxen, etoricoxib) — these reduce progesterone.
Address thyroid dysfunction — low T3 reduces progesterone.