• Progesterone is a hormone that prepares the lining of your uterus for pregnancy. 
• Each month, levels of progesterone rise after ovulation (the release of an egg) and help maintain a pregnancy.
• If the egg is not fertilised and pregnancy does not occur, levels of progesterone drop and menstrual bleeding begins.
• The progesterone test measures progesterone in a sample of blood. 
• It is used to assess ovulation, fertility and early pregnancy.
   

Progesterone is a hormone that plays an important role in the menstrual cycle and pregnancy.
Your menstrual cycle is regulated by a combination of different hormones, including oestrogen, progesterone, follicle stimulating hormone (FSH) and luteinising hormone.

Progesterone prepares the lining of your uterus for pregnancy which becomes rich in nutrients and blood vessels making it suitable for a fertilised egg to implant. Levels rise after ovulation – the time that the egg is released.

If pregnancy does not occur, progesterone levels fall, causing the uterine lining to break down and your period to begin. If pregnancy occurs, progesterone helps maintain conditions needed for the developing baby. It also helps prepare your breasts for breastfeeding, working with other hormones to develop the milk-producing tissues.

What happens monthly: 

• Oestrogen causes the lining of the uterus (endometrium) to grow.
• A surge in luteinising hormone (LH) causes the release of an egg from one of your two ovaries. 
• The corpus luteum, a small yellow mass of cells, forms in the ovary at the site where the egg was released and it begins to produce progesterone. 
• This progesterone prepares the uterus for the possible implantation of a fertilised egg. 
• If fertilisation does not occur, the corpus luteum degenerates, progesterone levels drop and menstrual bleeding begins. 
• If pregnancy occurs (a fertilised egg is implanted in the uterus) the corpus luteum continues to produce progesterone. After several weeks, the placenta replaces the corpus luteum as the main source of progesterone, producing relatively large amounts of the hormone throughout the rest of a normal pregnancy.
   

A progesterone test measures progesterone in a sample of your blood.

If you are not pregnant

Progesterone testing can be used if you have abnormal uterine bleeding. Progesterone helps in the normal build-up and shedding of the uterine lining after ovulation. If you do not ovulate normally, or do not produce enough progesterone, the lining can become unstable and shed irregularly, causing prolonged or heavy bleeding.  

Progesterone testing can help show whether you have ovulated and whether abnormal ovulation could be contributing to the bleeding. Results are usually interpreted alongside other tests that assess ovulation and other possible hormonal causes. These can include:

• Pregnancy test (hCG) – to exclude pregnancy as a cause of the bleeding. 
• FSH and LH – to assess ovarian function and ovulation. 
• Oestradiol – to assess ovarian hormone production. 
• TSH – to check for thyroid disease, which can affect menstrual bleeding. 
• Prolactin – because high prolactin can interfere with ovulation and menstrual cycles. 
• Full blood count (FBC) – to check for anaemia if bleeding is heavy or prolonged.

If you are pregnant

If you are in early pregnancy and have symptoms such as abdominal pain or spotting, measuring your progesterone levels together with levels of beta-human chorionic gonadotropin (β-hCG) can help assess whether you have an ectopic pregnancy or a pregnancy that is failing and could lead to miscarriage. However, progesterone and β-HCG testing cannot distinguish between these two conditions.

• If you have a high-risk pregnancy, your progesterone levels can be measured to help assess the health of the placenta and developing baby.
• If you have had difficulty maintaining a pregnancy in the past, your progesterone levels may be monitored because low levels can be associated with miscarriage.
• If you are having progesterone treatment to support an early pregnancy, regular testing may be used to check your progesterone levels and help assess how well the treatment is working.

If you are having difficulty becoming pregnant

Progesterone levels are measured as part of an infertility assessment:

• To check whether you are ovulating normally.
• If you are receiving fertility treatment to stimulate ovulation, to check whether and when ovulation has occurred.

Sample
Blood

Any preparation?
Speak with your doctors about any medications you are taking. Oestrogen and progesterone supplements may cause inaccurate results.

The timing of your test is important because progesterone levels change throughout your menstrual cycle. Levels are low before ovulation, rise after an egg is released, and fall again if pregnancy does not occur. Since progesterone levels vary predictably throughout the menstrual cycle, multiple measurements may be needed.

Progesterone results are interpreted according to why you are being tested, where you are in your menstrual cycle or pregnancy, and whether you are receiving fertility treatment. A single progesterone result rarely provides a diagnosis on its own because progesterone levels naturally fluctuate and laboratory reference intervals vary.

Progesterone is usually low during the first half of your menstrual cycle and rises after ovulation.
When progesterone is measured in the mid-luteal phase—about 7 days before your expected period:

• A raised progesterone level provides evidence that you have ovulated. The higher level reflects normal progesterone production by the corpus luteum. 
• A low progesterone level can mean that ovulation has not occurred. 
• Persistently low progesterone, together with irregular or absent periods, can help investigate problems with ovulation. 

There is no single progesterone concentration that reliably assesses the "quality" of ovulation or fertility. Your result needs to be interpreted according to the timing of your menstrual cycle and the laboratory's reference interval.
In pregnancy:

• A progesterone level within the expected range is generally reassuring and is consistent with a continuing pregnancy, but it cannot by itself confirm that the pregnancy is developing normally or that it is located within the uterus. 
• A low progesterone level can be associated with a pregnancy that is not developing normally, including miscarriage or ectopic pregnancy. However, progesterone alone cannot distinguish between these conditions. 
• Levels of progesterone will be naturally higher during pregnancies that involve multiple babies (twins, triplets, etc.) than those in which there is only one baby.
• Increased progesterone levels are also seen occasionally with luteal ovarian cysts, molar pregnancies and with a rare form of ovarian cancer.
• An intermediate or uncertain result often needs to be interpreted with serial β-hCG measurements and ultrasound. 

Reading your test report
Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.

Reference intervals - comparing your results to the healthy population

• Your results will be compared to reference intervals (sometimes called a normal range).
• Reference intervals are the range of results expected in healthy people.
• They are used to provide a benchmark for interpreting a patient's test results.
• When compared against them, your results may be flagged high or low if they sit outside this range.
• Some reference intervals are harmonised or standardised, which means all labs in Australia use them.
• Others are not because for these tests, labs are using different instruments and chemical processes to analyse samples.
• Always compare your lab results to the reference interval provided on the same report.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation.

Reference intervals for progesterone vary between laboratories in Australia because they use different measurement instruments. 

Progesterone testing is occasionally done in males if they are being investigated for fertility or adrenal gland problems. The results will be interpreted along with testosterone, LH, FSH and cortisol. Progesterone values in males are much lower than in females.

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.
You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.
Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?
   

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.
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