Progesterone ng/mL to nmol/L Converter

Progesterone in two units: the short answer

To convert progesterone from ng/mL to nmol/L, multiply by 3.18. To convert nmol/L back to ng/mL, divide by 3.18 (or multiply by 0.3145). A progesterone of 10 ng/mL is therefore about 31.8 nmol/L, and 30 nmol/L is about 9.4 ng/mL. Because ng/mL equals µg/L, a result in µg/L reads exactly like one in ng/mL. The converter above works in both directions and shows typical ranges for the follicular phase, the mid-luteal phase and early pregnancy.

Progesterone is measured mainly for two reasons: to check whether ovulation has occurred, and to assess early pregnancy or fertility treatment. In both situations, the thresholds quoted by clinics and guidelines are often in only one unit – "above 30 nmol/L" in the UK, "above 3 ng/mL" or "above 10 ng/mL" in the US – so converting correctly is the first step to reading the result. This guide covers the conversion, the hormone's role, ranges through the cycle and pregnancy, how timing changes the result and the pitfalls of interpretation.

What progesterone does

Progesterone is a steroid hormone made mainly by the corpus luteum – the structure that forms in the ovary from the follicle after it releases an egg. Smaller amounts are made by the adrenal glands, and from about the eighth to tenth week of pregnancy the placenta becomes the main source.

Its main roles are:

• transforming the lining of the uterus (endometrium) after ovulation so that it can receive an embryo
• maintaining early pregnancy and reducing uterine contractions
• raising body temperature slightly after ovulation (the basis of temperature charting)
• preparing breast tissue for milk production
• acting as a precursor for other steroid hormones, including cortisol and testosterone

Because progesterone is produced in substantial amounts only after ovulation, a raised level in the second half of the cycle is the standard laboratory evidence that ovulation has occurred.

ng/mL and nmol/L explained

• ng/mL (nanograms per milliliter) – the usual unit in the United States; identical to µg/L.
• nmol/L (nanomoles per liter) – the SI unit used in the UK, Europe, Australia and many other countries.

Why the factor is 3.18

Progesterone's molar mass is 314.5 g/mol. A concentration of 1 ng/mL is 1,000 ng per liter, which is 1,000 ÷ 314.5 = 3.18 nmol/L. Conversely, 1 nmol/L = 0.3145 ng/mL.

How to convert progesterone step by step

1. Check the unit on the report: ng/mL, µg/L or nmol/L.
2. For ng/mL (or µg/L) to nmol/L, multiply by 3.18.
3. For nmol/L to ng/mL, divide by 3.18.
4. Round to one decimal place.

Worked examples

• 1 ng/mL × 3.18 = 3.2 nmol/L – a typical follicular-phase level.
• 3 ng/mL × 3.18 = 9.5 nmol/L – a common US threshold suggesting that ovulation has occurred.
• 5 ng/mL × 3.18 = 15.9 nmol/L.
• 10 ng/mL × 3.18 = 31.8 nmol/L – often cited as consistent with a good ovulatory cycle and a common minimum in early pregnancy support.
• 30 nmol/L ÷ 3.18 = 9.4 ng/mL – the UK threshold commonly used to confirm ovulation.
• 16 nmol/L ÷ 3.18 = 5.0 ng/mL.
• 80 nmol/L ÷ 3.18 = 25.2 ng/mL – a typical early-pregnancy value.

Mental shortcut

Multiply ng/mL by 3 and add a bit, or divide nmol/L by 3 and subtract a bit. For 8 ng/mL: 8 × 3 = 24, plus about 1.5 = 25.5 nmol/L (exact: 25.4).

Progesterone conversion chart

Normal progesterone ranges

Through the menstrual cycle

Laboratory ranges vary, and luteal values in particular fluctuate from hour to hour.

Pregnancy

Progesterone rises through pregnancy. Typical ranges are roughly:

• First trimester: about 10–44 ng/mL (32–140 nmol/L)
• Second trimester: about 20–80 ng/mL (64–255 nmol/L)
• Third trimester: about 55–300 ng/mL or more (175–955 nmol/L or more)

These ranges overlap widely, and progesterone alone is not used to date a pregnancy or to judge whether it is healthy. Ultrasound and serial hCG measurements are the main tools.

Confirming ovulation: the mid-luteal progesterone test

The mid-luteal progesterone test – often called the "day 21 progesterone" – is the standard laboratory way to confirm ovulation.

Timing matters more than the day number

The test should be taken about seven days before the expected start of the next period, not on day 21 by default. Day 21 is correct only for a 28-day cycle. For a 35-day cycle, the right day is around day 28; for a 24-day cycle, around day 17. Testing too early or too late can give a falsely low result in a cycle that was ovulatory. NICE fertility guidance specifically advises adjusting the timing for cycle length and repeating the test weekly, starting at the mid-luteal point, for women with irregular cycles until the next period begins.

Thresholds

• UK (NICE and common laboratory practice): a mid-luteal progesterone above about 30 nmol/L (9.4 ng/mL) is taken as confirming ovulation. Some laboratories use lower values, such as 16–25 nmol/L, as consistent with ovulation.
• US practice: levels above about 3 ng/mL (9.5 nmol/L) indicate that ovulation has occurred, while many fertility clinics consider 10 ng/mL (32 nmol/L) or more to reflect a robust luteal phase.

The thresholds look like they disagree – 30 nmol/L versus 3 ng/mL – but after conversion they describe different questions. A value of 3 ng/mL (about 10 nmol/L) shows that ovulation happened; a value around 10 ng/mL (about 30 nmol/L) suggests ovulation with good luteal function. Any value in between should be interpreted in light of timing.

Why one low result is not conclusive

Progesterone from the corpus luteum is released in pulses, so a single sample can vary considerably over a few hours. A low result taken at the right time in a regular cycle may still reflect normal ovulation. Many clinicians repeat the test in another cycle before drawing conclusions, and they consider other evidence such as regular cycles, ovulation predictor kits and ultrasound tracking.

Progesterone in early pregnancy

Progesterone is sometimes measured in early pregnancy, especially when there is pain or bleeding and the location of the pregnancy is not yet clear on ultrasound (a pregnancy of unknown location). Broadly:

• A very low progesterone, for example below about 5 ng/mL (16 nmol/L), is strongly associated with a pregnancy that is not viable, either a miscarriage or an ectopic pregnancy.
• A level above about 25 ng/mL (80 nmol/L) is strongly associated with a viable intrauterine pregnancy.
• Values in between are common and are not diagnostic on their own.

Progesterone is never used alone to make decisions about treatment of a pregnancy; it supplements ultrasound and hCG trends.

Progesterone supplements in pregnancy

Progesterone treatment is used in several situations: as luteal support in IVF, to reduce preterm birth in some women with a short cervix, and – following the PRISM trial – in some women with bleeding in early pregnancy and a history of previous miscarriage, where it modestly increased live births. NICE now recommends offering vaginal micronised progesterone to women with early pregnancy bleeding who have had a previous miscarriage. Whether a "low" blood level by itself justifies supplementation is not established, and blood levels with vaginal progesterone may underestimate the amount reaching the uterus.

Progesterone in fertility treatment

During IVF and frozen embryo transfer, progesterone is given to support the uterine lining. Some clinics measure blood progesterone around the time of transfer, and several studies have associated levels below about 10 ng/mL (32 nmol/L) in hormone-replacement frozen transfer cycles with lower pregnancy rates; some clinics then increase the dose. Practice varies, and the unit used by your clinic determines which threshold applies. On the other hand, a progesterone that rises too early – before egg collection in a fresh IVF cycle, typically above about 1.5 ng/mL (4.8 nmol/L) on the day of the trigger injection – can reduce the chance of implantation in that cycle, and some clinics then freeze all embryos for later transfer.

Low and high progesterone

Low progesterone

A low mid-luteal progesterone usually means no ovulation occurred in that cycle (anovulation) or that the test was mistimed. Common causes of anovulation include polycystic ovary syndrome (PCOS), hypothalamic amenorrhoea from low body weight, excessive exercise or stress, thyroid disease, high prolactin, the perimenopause and premature ovarian insufficiency. The concept of an isolated "luteal phase defect" is controversial, and the American Society for Reproductive Medicine has stated that there is no reliable way to diagnose it and that it has not been proven to cause infertility as an independent condition.

High progesterone

A higher than expected progesterone is most often due to pregnancy, a multiple pregnancy, progesterone supplements or ovarian stimulation. Rarer causes include ovarian cysts, molar pregnancy and congenital adrenal hyperplasia, in which a related hormone (17-hydroxyprogesterone) is usually tested instead.

Home ovulation tracking and progesterone

Several home methods track the effects of progesterone rather than the blood level itself:

• Basal body temperature charting – progesterone raises resting temperature by about 0.2–0.5 °C after ovulation. A sustained rise for several days indicates that ovulation has probably occurred, but only in retrospect.
• Urine PdG tests – pregnanediol glucuronide (PdG) is the main urinary breakdown product of progesterone. Home tests detect a rise in PdG after ovulation. They measure a different substance in a different fluid, so their results cannot be converted into blood progesterone values.
• LH test strips – detect the surge of luteinizing hormone that precedes ovulation by about 24–36 hours. They predict ovulation but do not confirm it.

These methods can help with timing intercourse or a blood test, but they do not replace a correctly timed blood progesterone where a clinical decision depends on it.

Progesterone and menopause hormone therapy

Women with a uterus who take oestrogen as menopausal hormone therapy need a progestogen as well, to protect the lining of the womb from overgrowth (endometrial hyperplasia) and cancer. Options include micronised progesterone (taken by mouth or vaginally), synthetic progestins, or a levonorgestrel intrauterine system. Blood progesterone levels are not used to monitor this treatment: oral micronised progesterone produces variable blood levels and is largely metabolised, and adequacy is judged by the regimen and by investigating any unexpected bleeding, not by a blood test.

Some clinics and online services offer "bioidentical" hormone treatment adjusted to blood or saliva progesterone levels. Major menopause societies advise against compounded hormones and against dose adjustment based on saliva testing, because these approaches lack evidence and standardisation.

Comparing results from different clinics

A woman who has a mid-luteal result of 24 nmol/L at a UK clinic and 9 ng/mL at a US clinic in another cycle might think the second is much lower. Converted, 9 ng/mL is 28.6 nmol/L, so the two results are similar; both show ovulation, slightly below the UK 30 nmol/L benchmark. When comparing cycles, also check the day of each test relative to the following period.

What affects progesterone results

• Cycle timing – the most important factor. A sample taken a few days too early or too late can be low in an ovulatory cycle.
• Pulsatile secretion – luteal progesterone can vary several-fold within hours.
• Hormonal contraceptives – most prevent ovulation, so progesterone stays low. Synthetic progestins in contraceptives usually do not register on progesterone assays.
• Progesterone treatment – levels depend on the route (vaginal, injection, oral) and the timing after the last dose.
• Assay method – immunoassays may cross-react with other steroids; differences between laboratories of 10–20% are common.
• Biotin supplements can interfere with some immunoassays.

When to see a doctor

See a doctor if you have been trying to conceive for 12 months (or six months if you are 35 or older), if your periods are absent, very irregular or very far apart, or if repeated correctly timed mid-luteal progesterone results are low. In early pregnancy, seek prompt medical care for bleeding, one-sided abdominal pain, shoulder-tip pain, dizziness or fainting, which can be signs of an ectopic pregnancy – a progesterone result should never delay urgent assessment.