Biomarker Glossary
Progesterone
Progesterone is a key female reproductive hormone produced mainly by the ovaries after ovulation. A progesterone blood test, classically taken on day 21 of the menstrual cycle, is the standard UK test for confirming ovulation, investigating fertility and assessing luteal phase function.
Also known as: P4
Progesterone is most informative when read alongside related markers like Oestradiol and Testosterone. A single number rarely tells the whole story. If your reading sits outside the typical range, share the full report with your GP or healthcare professional before drawing conclusions.
What is Progesterone?
Progesterone is produced by the corpus luteum (the structure left after the ovary releases an egg) during the second half of the menstrual cycle. It prepares the uterine lining for a possible pregnancy and supports early pregnancy if conception occurs.
If no pregnancy occurs, the corpus luteum breaks down, progesterone falls, and the lining sheds as a period. If pregnancy occurs, the corpus luteum (and later the placenta) maintains progesterone production.
Progesterone also has roles beyond reproduction: calming the nervous system, supporting sleep and mood, and balancing the effects of oestrogen on breast and uterine tissue.
Why test Progesterone?
- To confirm ovulation when investigating fertility.
- To assess luteal phase function (the second half of the cycle).
- To monitor progesterone therapy in HRT or fertility treatment.
- To investigate PMS or PMDD.
- To assess perimenopause alongside oestradiol, FSH and LH.
To confirm ovulation when investigating fertility.
Progesterone normal range (UK)
| Result | What it means |
|---|---|
| Day 21 (or 7 days before expected period): above 30 nmol/L | Confirms ovulation occurred |
| Below 16 nmol/L on day 21 | No ovulation or poor luteal function |
| Follicular phase: below 3 nmol/L | Normal |
| Luteal phase: 5 to 60 nmol/L | Normal (peaks around day 21) |
| Postmenopause: below 2 nmol/L | Typical |
| Pregnancy: rises dramatically from first trimester onwards | Normal |
Timing is essential. Day 21 of a 28 day cycle is the classic test point, when progesterone should peak. If your cycle is longer or shorter, test 7 days before your expected period. A single below threshold reading may need repeating to confirm an anovulatory cycle.
About these ranges. The ranges above are typical UK clinical lab ranges aligned to NHS and Royal College of Pathologists guidance. Your Chxhealth report will show the specific reference range used by our partner lab, Randox, for each marker. Lab ranges vary slightly between providers and assays. Always interpret your results in the context of the range printed on your own report.
What causes high Progesterone?
- Pregnancy (high levels are normal)
- Progesterone or progestin medication (HRT, contraceptives)
- Ovarian cyst
- Congenital adrenal hyperplasia (rare)
- Adrenal disorders
What causes low Progesterone?
- Anovulation (no egg released this cycle)
- Luteal phase deficiency (corpus luteum produces too little)
- Menopause or perimenopause
- Stress and chronic illness
- Functional hypothalamic amenorrhoea (low body fat, excessive exercise)
- Pituitary disorders
Symptoms of high Progesterone
- Mostly seen during pregnancy or with progesterone medication.
- Possible drowsiness, bloating, breast tenderness, mood changes.
Symptoms of low Progesterone
- Irregular or absent periods
- Difficulty conceiving
- Recurrent miscarriage in some cases
- Heavy or prolonged periods
- PMS and PMDD symptoms (irritability, breast tenderness, mood swings)
- Sleep disturbance
- Anxiety
- Spotting before periods
How is Progesterone tested?
Progesterone is measured from a blood sample. For ovulation confirmation, test on day 21 of a 28 day cycle, or 7 days before your expected period if your cycle is different.
A single reading is sufficient for most purposes. For research grade confirmation of ovulation, some clinicians test on days 19, 21 and 23.
Chxhealth samples are analysed by Randox, a UK laboratory accredited by UKAS. Results return in 3 to 5 working days.
How to support healthy Progesterone levels
- Maintain a healthy body weight. Very low body fat or rapid weight loss disrupts ovulation and progesterone production.
- Manage stress. Chronic stress diverts hormone production away from progesterone.
- Eat enough overall calories and healthy fats. Hormones are built from cholesterol.
- Prioritise sleep, which supports the entire hormonal axis.
- If progesterone is consistently low and you are trying to conceive, speak to a fertility specialist. Chxhealth does not prescribe.
These are general lifestyle suggestions. Chxhealth is an information service. For personal medical advice, please speak to a healthcare professional.
Chxhealth panels that test Progesterone
6 Chxhealth biomarker panels include Progesterone. Each is analysed by Randox, a UK laboratory accredited by UKAS. Reports are delivered in 3 to 5 working days.
- Advanced GP3
- Endocrinology
- Fertility Panel
- Hormonal Health
- Elite Biohacking
- Athletic Performance Panel
Progesterone FAQs
What is a day 21 progesterone test?
The standard UK test for confirming ovulation. Progesterone peaks about 7 days after ovulation, which is typically day 21 in a 28 day cycle. A level above 30 nmol/L on day 21 confirms ovulation has occurred.
What if my cycle is not 28 days?
Test 7 days before your expected next period. For a 30 day cycle, that means day 23. For a 35 day cycle, day 28.
Can low progesterone cause miscarriage?
Progesterone supports early pregnancy. Low progesterone is associated with miscarriage in some studies, although the relationship is complex. Speak to a fertility specialist for individual advice.
Why is progesterone important in perimenopause?
Progesterone falls earlier than oestradiol during perimenopause. Many perimenopausal symptoms (sleep problems, anxiety, heavy bleeding, breast tenderness) reflect this imbalance. Progesterone is part of many HRT regimens.
Can progesterone affect mood?
Yes. Progesterone has a calming effect on the brain. Falling progesterone before a period is one driver of PMS and PMDD. Progesterone therapy can help in some cases under medical supervision.
Often tested with Progesterone
The biomarkers below are commonly investigated alongside Progesterone because they reveal connected aspects of the same physiological picture:
- Oestradiol: Cycle-phase pairing is essential.
- Testosterone: Full hormone picture benefits from all three.
- AMH: AMH adds ovarian reserve context.
Choose the right test for your goal
If you are reading about Progesterone because of a specific health goal, our buying guides walk you through which Chxhealth panels fit:
- Best blood test for women's hormones
- Best blood test for fertility planning
- View all blood test guides
Sources and further reading
This page is informed by guidance from the NHS, NICE, Royal College of Pathologists and other UK authoritative bodies. For deeper detail or to verify the information, see:
- NHS: Fertility tests
- Society for Endocrinology: Progesterone
- British Fertility Society
- Lab Tests Online UK: Progesterone
About this page. Last reviewed: 13 May 2026. Next scheduled review: May 2027. This page has not yet been independently reviewed by a clinician. It is written from authoritative UK medical guidance (NHS, NICE, Royal College of Pathologists, peer-reviewed sources) but has not undergone formal clinical sign off.
Important. Chxhealth is a UK information service. We do not diagnose, treat or prescribe. The reference ranges and information on this page are general educational content and should not be used as a substitute for advice from a qualified healthcare professional. For any concerns about your health or results, please speak to your GP or another healthcare professional.