Progesterone is a hormone produced by the ovaries that is responsible for regulating the menstrual cycle and preparing the body for pregnancy.
Progesterone is also produced in small quantities by the testes and adrenal glands in men and people assigned male at birth (AMAB) and plays an important role in the production of spermatozoa (sperm) and maintaining a healthy prostate.
Progesterone levels can be high due to pregnancy, congenital adrenal hyperplasia, or ovarian cancer, or low due to menopause, polycystic ovary syndrome, or hypothyroidism. It is important to consult an endocrinologist, gynecologist, or urologist for further testing to determine the cause of abnormal progesterone levels and arrange for the best treatment.
Main functions
Progesterone plays an important role in:
1. Preparing the body for pregnancy
Progesterone is a very important hormone for preparing the body for pregnancy, helping to prevent the fertilized egg from being rejected by the body.
When fertilization occurs, progesterone is released by the corpus luteum to stimulate thickening of the uterine lining and increase blood flow to the uterus, allowing implantation of the embryo to occur and bringing more nutrients to the area.
2. Preventing rejection of the fetus
During pregnancy, progesterone helps prevent the mother's body from rejecting the fetus.
This is because progesterone modifies the immune system response so that the body does not attack the fetus, thinking it is an outside invader.
3. Sustaining the pregnancy
Progesterone helps sustain a healthy pregnancy by preventing uterine contractions that could result in miscarriage or premature birth.
As pregnancy advances, progesterone starts to be produced by the placenta, continuing to rise throughout the pregnancy until reaching a peak in the third trimester.
4. Preparing the body for breastfeeding
Progesterone also helps prepare the body for future breastfeeding.
This is because progesterone, along with estrogen and prolactin, stimulates the development of the mammary glands during pregnancy.
5. Supporting fetal development
During pregnancy, adequate progesterone levels are also important for supporting fetal development.
This is because progesterone stimulates the production of blood vessels in the uterus and improves blood flow to and from the placenta, allowing for the delivery of nutrients to the fetus and the removal of waste.
Progesterone also helps regulate the fetal adrenal gland to allow for adequate hormone production after birth. It also helps protect the developing neurons and promote maturation of the fetal lungs.
6. Regulating the menstrual cycle
Progesterone also serves to regulate the menstrual cycle, preparing for a possible pregnancy.
Progesterone production is highest during the luteal phase of the menstrual cycle, which begins after ovulation with the formation of the corpus luteum. Learn more about ovulation tests.
If fertilization does not occur, progesterone levels start to fall, triggering menstruation.
7. Maintaining the integrity of the nervous system
Progesterone serves to maintain the integrity of the nervous system by playing an important role in the synthesis of myelin sheaths, which cover neurons and allow for the transmission of nerve impulses.
8. Preventing osteoporosis
Progesterone, along with estrogen, is important for maintaining bone density and strengthening the bones, thereby helping to prevent osteoporosis.
9. Producing sperm
While only produced in small quantities in men, progesterone is important for the production of spermatozoa (sperm).
This is because progesterone is a precursor to testosterone, a sex hormone important for fertility.
10. Maintaining a healthy prostate
Progesterone in men also plays an important role in prostate health.
This is because progesterone binds to receptors on the prostate to prevent uncontrolled cell division that can lead to benign prostatic hyperplasia (enlarged prostate).
Indications for testing
Progesterone testing is typically recommended for women and people assigned female at birth (AFAB) in the following situations:
- Planning a pregnancy;
- Irregular periods;
- Heavy menstrual bleeding (menorrhagia);
- Monitoring of a high risk pregnancy;
- Determining the risk of miscarriage or premature birth;
- Diagnosing an ectopic pregnancy;
- Investigating causes of infertility or difficulty getting pregnant;
- Evaluating the efficacy of fertility treatments.
Blood progesterone levels can also be used to help diagnose ovarian cancer and adrenal gland disorders.
Progesterone tests may be ordered as part of prenatal care and repeated several times if shown to be decreasing between visits.
Progesterone tests cannot be used to confirm a pregnancy, however. If you think you might be pregnant, a pregnancy test to detect the presence of beta hCG in the body is recommended instead.
Preparing for the test
When preparing for a progesterone test, make sure to:
- Let your doctor know about all medications you are taking;
- Stop taking medications containing progestins, such as combined and progestin-only birth control pills;
- Avoid having an X-ray done during the 7 days prior to the test;
- Schedule the test for about 7 days post ovulation, as this is the time when progesterone levels are naturally the highest.
Your provider may also order a progesterone test to be drawn at a different point in your cycle, such as before ovulation, to see if progesterone levels remain elevated throughout your cycle.
Preparation is important to guarantee accurate results that are not influenced by other factors.
How the test is done
A progesterone test involves a simple blood draw to collect a blood sample to be analyzed in the lab.
Reference values
Progesterone levels in the blood vary based on age, sex, and phase of the menstrual cycle:
Blood progesterone levels may vary depending on the lab performing the test.
Results should always be interpreted by a gynecologist, urologist, or endocrinologist in order to better understand whether abnormal values are a normal variant or if they could be caused by certain health conditions.
High progesterone
High progesterone levels can be caused by ovulation or pregnancy, which is normal.
Progesterone levels may be significantly elevated in twin pregnancies.
Certain health conditions, like polycystic ovary syndrome, molar pregnancy, and ovarian cancer, can also cause levels of progesterone to be elevated.
High progesterone can also be caused by congenital adrenal hyperplasia, adrenal gland cancer, or the use of combined or progestin-only contraception.
Symptoms of high progesterone
The most common symptoms of high progesterone are:
- Swollen breasts or increased breast sensitivity;
- Excessive tiredness or fatigue;
- Distended abdomen;
- Anxiety or depression;
- Low libido.
High progesterone can also cause fluid retention, weight gain, headaches, irregular periods, and alterations in menstrual flow.
Low progesterone
Low progesterone can be caused by conditions like polycystic ovary syndrome, luteal phase deficiency, or perimenopause.
Low progesterone in pregnancy may indicate ectopic pregnancy, miscarriage, or increased risk for miscarriage. It may also be a sign of preeclampsia.
Symptoms of low progesterone
The most common symptoms of low progesterone are:
- Absence of ovulation or menstruation;
- Irregular periods;
- Hot flashes;
- Mood changes;
- Frequent headaches;
- Difficulty getting pregnant.
Low progesterone may also cause abnormal uterine bleeding in non-pregnant people and spotting during pregnancy.
Low progesterone in pregnancy
Low progesterone levels at the beginning of pregnancy may increase the risk for miscarriage.
They may also be a sign of an ectopic pregnancy, which needs to be treated right away in order to prevent serious complications.
Progesterone levels that start to decline toward the end of the second trimester can be a sign of an increased risk for premature birth.
Treatment options
Treatment for abnormal progesterone levels is usually only done when numbers are lower than normal.
In these cases, a doctor may prescribe progesterone in pill form, such as Prometrium, especially for women who are having difficulty getting pregnant.
Progesterone may also be used in the first trimester to help prevent miscarriage in people with a history of recurrent miscarriages and in cases of threatened miscarriage or luteal phase deficiency.
Additionally, an OBGYN may prescribe progesterone vaginal suppositories for women with a history of preterm birth and a short cervix.
Progesterone may also be used in combination with estrogen as part of hormonal replacement therapy (HRT) for menopause.
Side effects
The use of hormones like progesterone can result in side effects like weight gain, generalized swelling, fluid retention, fatigue, breast tenderness, and irregular periods.
Some people may also experience increased appetite, frequent headaches, fever, and difficulty sleeping.
Progesterone treatments should be avoided in people with peripheral artery disease, breast cancer, abnormal uterine bleeding, and liver problems.
Natural remedies
Ways to stimulate the natural production of progesterone in the body include:
- Drinking turmeric, thyme, or oregano tea;
- Increasing intake of foods high in vitamin B6, such as beef liver, bananas, and salmon;
- Taking magnesium supplements (in consultation with a registered dietitian);
- Choosing foods high in protein;
- Following a diet rich in fruits and vegetables, especially green leafy vegetables like spinach.
Choosing organic foods whenever possible may also help increase progesterone production, as some chemicals used in processed or packaged foods may affect normal hormone production in the body.