What is being tested?

This test measures the level of progesterone in the blood. Progesterone is a steroid hormone whose main role is to help prepare a woman’s body for pregnancy; it works together with several other female hormones.

On a monthly basis, the hormone oestrogen causes the endometrium (the lining of the womb, or uterus) to grow and replenish itself, while a surge in luteinising hormone (LH) leads to the release of an egg from one of the two ovaries. The corpus luteum (a small yellow mass of cells) then forms in the ovary at the site where the egg was released and begins to produce progesterone. This progesterone stops endometrial growth and 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 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.

How is it used?

Since progesterone levels vary predictably throughout the menstrual cycle, multiple measurements can be used to help diagnose infertility problems. Progesterone can be measured to determine whether or not a woman has ovulated (released an egg from the ovary), to determine when ovulation occurred and to monitor the success of medically induced ovulation.

In early pregnancy, progesterone measurements may be used, along with human chorionic gonadotropin (hCG) testing, to help diagnose an ectopic pregnancy or failing pregnancy (one leading to miscarriage), although these tests will not differentiate between the two conditions. Progesterone levels may also be measured throughout a high-risk pregnancy to help evaluate placental and fetal health.

Progesterone levels may be monitored in women who have trouble maintaining a pregnancy, as low levels of the hormone can lead to miscarriage. If a woman is receiving progesterone injections to help support her early pregnancy, her progesterone levels may be monitored on a regular basis to help determine the effectiveness of that treatment.

In women who are not pregnant, progesterone levels may be used, along with other tests, to help determine the cause of abnormal uterine bleeding.

When is it requested?

Progesterone levels are measured:

• As part of an infertility assessment, when a woman is having trouble getting pregnant and the doctor wants to verify that she is ovulating normally
• To determine if and when ovulation has occurred following drug therapy to induce ovulation
• When symptoms, such as abdominal pain and spotting, suggest an ectopic pregnancy or threatened miscarriage
• To monitor the effectiveness of treatment when a pregnant woman requires progesterone injections to help maintain her pregnancy
• To monitor placental and fetal health during a high-risk pregnancy
• When a non-pregnant woman is experiencing abnormal uterine bleeding.

What does the result mean?

Interpretation of progesterone test results requires knowledge of where a woman is in her menstrual cycle or pregnancy. Progesterone levels usually start to rise when an egg is released from the ovary, continue to rise for several days, and then either continue to rise with early pregnancy or fall to start menstruation.

If progesterone levels do not rise and fall on a monthly basis, a woman may not be ovulating or having menstrual periods. If levels do not rise normally during an early pregnancy, the pregnancy may be ectopic and/or may be failing. If serial measurements do not show increasing progesterone levels over time, there may be problems with the placenta and foetus.

Levels of progesterone will be naturally higher during pregnancies that involve multiples (twins, triplets, etc.) than those in which there is only one foetus.

Increased progesterone levels are also seen occasionally with luteal ovarian cysts, molar pregnancies, and with a rare form of ovarian cancer.

Increased levels are occasionally due to an overproduction of progesterone by the adrenal glands.

In late pregnancy, low levels of progesterone may be associated with toxaemia and pre-eclampsia (pregnancy-induced high blood pressure).

Is there anything else I should know?

Taking oestrogen and progesterone supplements may cause inaccurate results.

Common questions

• Are men tested for progesterone?

No. Progesterone does not have an established role in males.

• Are there other uses for progesterone?

Yes. Progesterone is sometimes used in hormone replacement therapy (HRT) for menopausal women. Other types of HRT use synthetic progestins  which are similar in structure to natural progesterone and act similarly to progesterone in the body.  If you have had your uterus removed (hysterectomy), your HRT will most likely not include progesterone.  

Most progestogen only contraceptive pills contain a synthetic progestin rather than progesterone.

More information

RCPA Manual: Progesterone