Progesterone
Progesterone is produced by the corpus luteum after ovulation. It prepares the uterine lining for implantation and supports early pregnancy. Testing confirms ovulation occurred (unlike LH kits that only predict it) and assesses luteal phase adequacy. Low mid-luteal progesterone means either no ovulation or luteal phase deficiency — both treatable causes of infertility. Timing critical: test ~7 days after ovulation (day 21 of 28-day cycle). Men produce small amounts but testing is rarely needed.
Progesterone is the hormone that prepares the body for pregnancy and maintains early pregnancy. After ovulation, the corpus luteum (the structure left behind when the egg is released) produces progesterone, which transforms the uterine lining into a welcoming environment for embryo implantation. If pregnancy occurs, progesterone continues supporting it; if not, progesterone drops, triggering menstruation.
Why does this matter? Progesterone testing serves two main purposes: confirming that ovulation occurred and assessing whether progesterone levels are adequate to support pregnancy. Low progesterone in the luteal phase (after ovulation) can contribute to infertility or early pregnancy loss. Testing helps identify this treatable problem and guides supplementation when needed.
While progesterone is primarily a female reproductive hormone, men produce small amounts in the adrenal glands and testes. However, progesterone testing in men is uncommon and only performed in specific clinical situations.
Key Benefits of Testing
Progesterone testing provides definitive evidence that ovulation occurred. Unlike ovulation predictor kits that detect the LH surge before ovulation, progesterone testing confirms ovulation actually happened by measuring the hormone produced afterward. This distinction is clinically important — some women have LH surges without releasing an egg.
Testing also assesses luteal phase adequacy. If progesterone is too low after ovulation, the uterine lining may not support implantation or early pregnancy. Identifying luteal phase deficiency allows for progesterone supplementation that may improve fertility outcomes.
What Does This Test Measure?
The progesterone test measures the concentration of progesterone hormone in your blood. Progesterone is a steroid hormone produced primarily by the corpus luteum after ovulation and by the placenta during pregnancy. The adrenal glands produce small amounts in both sexes.
The Progesterone Cycle in Women
Progesterone levels follow a predictable pattern through the menstrual cycle. During the follicular phase (from menstruation until ovulation), progesterone is very low — there’s no corpus luteum producing it. After ovulation, the corpus luteum forms and begins producing progesterone, which rises rapidly over the next several days. Levels peak about 7 days after ovulation (around day 21 of a 28-day cycle), then decline if pregnancy doesn’t occur, triggering menstruation.
This pattern means timing is critical for testing. A mid-luteal phase sample (about 7 days after ovulation) captures peak progesterone and best confirms ovulation occurred.
What Progesterone Does
Progesterone has several essential functions in reproduction. It transforms the estrogen-primed uterine lining into a secretory endometrium ready for implantation. It maintains the uterine lining during early pregnancy until the placenta takes over progesterone production around weeks 8-10. It thickens cervical mucus, creating a barrier to additional sperm and bacteria. It also has systemic effects including raising body temperature (the basis of temperature tracking for fertility) and affecting mood and sleep.
Progesterone in Pregnancy
During pregnancy, progesterone levels rise dramatically. The corpus luteum produces progesterone for the first 8-10 weeks, after which the placenta becomes the main source. Adequate progesterone is essential for maintaining pregnancy — it keeps the uterus relaxed and prevents contractions that could lead to miscarriage.
Progesterone in Men
Men produce small amounts of progesterone in the adrenal glands and testes. It serves as a precursor for other hormones including testosterone and cortisol. Progesterone testing in men is rarely performed clinically but may be checked in specific situations like congenital adrenal hyperplasia or certain hormone-producing tumors.
Why This Test Matters
Confirms Ovulation
Elevated mid-luteal progesterone is the gold standard for confirming ovulation occurred. While ovulation predictor kits detect the LH surge that precedes ovulation, they don’t confirm the egg was actually released. Some women have LH surges without ovulating (luteinized unruptured follicle syndrome). Progesterone testing provides definitive proof that ovulation happened.
Assesses Luteal Phase Function
The luteal phase is the critical window when implantation occurs. If the corpus luteum doesn’t produce enough progesterone (luteal phase deficiency), the uterine lining may not adequately support implantation or early pregnancy. Symptoms may include short cycles (less than 10 days from ovulation to period), spotting before the period, or early pregnancy loss. Progesterone testing identifies this treatable problem.
Supports Fertility Treatment
During fertility treatments, progesterone monitoring helps ensure adequate luteal support. Many IVF protocols include progesterone supplementation because the egg retrieval process disrupts normal corpus luteum function. Testing confirms supplementation is achieving adequate levels.
Monitors Early Pregnancy
In early pregnancy, progesterone levels provide information about pregnancy viability. While progesterone alone cannot diagnose a healthy pregnancy, very low levels in early pregnancy may indicate increased risk of miscarriage or ectopic pregnancy. Serial measurements showing rising progesterone are more reassuring than a single value.
Evaluates Abnormal Bleeding
In women with irregular or heavy bleeding, progesterone helps determine whether ovulation is occurring. Anovulatory cycles (cycles without ovulation) lack the progesterone that normally stabilizes the uterine lining, often resulting in unpredictable or heavy bleeding.
Value of Testing Before Problems Arise
For women planning pregnancy, confirming ovulation and adequate luteal function before actively trying to conceive can save months of frustration. If cycles appear regular but progesterone testing reveals anovulation or luteal phase deficiency, this can be addressed proactively. Women with irregular cycles, history of hormonal problems, or approaching their mid-30s may particularly benefit from baseline assessment. Identifying issues early allows time for treatment optimization before the pressure of the fertility clock intensifies.
What Can Affect Progesterone Levels?
Causes of High Progesterone
- Pregnancy — progesterone rises significantly
- Ovulation (normal mid-luteal elevation)
- Ovarian cysts, particularly corpus luteum cysts
- Congenital adrenal hyperplasia (certain types)
- Ovarian or adrenal tumors producing progesterone (rare)
- Progesterone supplementation or hormone therapy
Causes of Low Progesterone
- Anovulation — no ovulation means no corpus luteum to produce progesterone
- Testing in the follicular phase (before ovulation) — progesterone is normally low
- Luteal phase deficiency — corpus luteum doesn’t produce enough
- Threatened miscarriage or ectopic pregnancy
- Menopause — ovulation no longer occurs
- Polycystic ovary syndrome (when anovulatory)
- Hypothalamic amenorrhea
- Hyperprolactinemia
Timing Is Critical
Progesterone varies dramatically through the menstrual cycle. Testing too early (before ovulation) will show low levels even in women who ovulate normally. Testing too late (just before menstruation) may catch falling levels. For confirming ovulation, testing should occur about 7 days after suspected ovulation — typically around day 21 of a 28-day cycle, but adjusted based on actual cycle length.
If your cycles are longer than 28 days, subtract 14 from your typical cycle length to estimate ovulation day, then test 7 days later. For irregular cycles, testing based on other ovulation signs (temperature shift, LH surge) may be more accurate.
When Should You Get Tested?
Confirming ovulation: When trying to conceive and wanting to verify ovulation is occurring. Test approximately 7 days after expected ovulation.
Infertility evaluation: Progesterone is a standard part of fertility workup to assess ovulatory function and luteal phase adequacy.
Recurrent pregnancy loss: Low progesterone may contribute to early miscarriage. Testing helps identify if supplementation might help.
Irregular menstrual cycles: Helps determine if cycles are ovulatory or anovulatory.
During fertility treatment: Monitors response to ovulation induction and adequacy of luteal support.
Early pregnancy monitoring: When there’s concern about pregnancy viability, such as after prior losses or with concerning symptoms.
Abnormal uterine bleeding: Helps evaluate whether anovulation is contributing to irregular bleeding patterns.
Understanding Your Results
Progesterone interpretation depends entirely on when in the cycle the test was performed. A value that’s normal at one point may be abnormal at another.
Follicular Phase (Before Ovulation)
Progesterone is normally very low before ovulation. Low levels at this time don’t indicate any problem — there’s simply no corpus luteum producing progesterone yet.
Mid-Luteal Phase (About 7 Days After Ovulation)
This is the key timing for evaluating ovulation and luteal function. Elevated progesterone at this point confirms ovulation occurred. The higher the level, the more confident the confirmation. Low mid-luteal progesterone suggests either anovulation (no ovulation occurred) or luteal phase deficiency (ovulation occurred but the corpus luteum isn’t producing adequate progesterone).
Early Pregnancy
Progesterone levels in early pregnancy vary widely, and a single value has limited predictive ability. Very low levels may raise concern, but progesterone alone cannot diagnose a healthy or unhealthy pregnancy. Trends over time (rising versus falling) provide more information. Progesterone is typically interpreted alongside hCG levels and ultrasound findings.
Postmenopausal
After menopause, progesterone is consistently low because ovulation no longer occurs. This is normal and expected.
What to Do About Abnormal Results
For Low Mid-Luteal Progesterone
Confirm timing was correct. If the test was done at the wrong cycle phase, results may be misleadingly low. Repeat testing with proper timing if there’s uncertainty.
Distinguish anovulation from luteal deficiency. If progesterone is very low, ovulation likely didn’t occur. If progesterone is detectable but lower than optimal, ovulation occurred but the corpus luteum may be underperforming.
Evaluate underlying causes of anovulation: PCOS, thyroid dysfunction, hyperprolactinemia, hypothalamic amenorrhea, and other conditions can cause anovulation. Addressing the underlying cause may restore normal cycles.
Consider progesterone supplementation if trying to conceive with confirmed luteal phase deficiency. Supplementation beginning after ovulation may improve the uterine environment for implantation.
For Low Progesterone in Early Pregnancy
Interpret with caution. Low progesterone doesn’t necessarily predict miscarriage, and normal progesterone doesn’t guarantee a healthy pregnancy.
Consider additional testing including hCG levels (serial measurements to check for appropriate rise) and ultrasound when timing is appropriate.
Progesterone supplementation is commonly prescribed when early pregnancy progesterone is low, particularly after fertility treatment or in women with history of recurrent loss. Evidence for benefit in spontaneous pregnancies is less clear, but supplementation is generally considered safe.
For High Progesterone
Check pregnancy status if elevated progesterone is unexpected — pregnancy causes significant elevation.
Evaluate for ovarian cysts if progesterone is high outside of pregnancy. Corpus luteum cysts can produce excess progesterone.
Review medications — progesterone supplementation or certain hormonal treatments elevate levels.
Related Health Conditions
Luteal Phase Deficiency
When the corpus luteum doesn’t produce enough progesterone, the uterine lining may not adequately support implantation or early pregnancy. Symptoms include short luteal phases (less than 10 days from ovulation to period), premenstrual spotting, and difficulty conceiving or maintaining early pregnancy. Progesterone supplementation is the primary treatment.
Anovulation
Cycles without ovulation produce no corpus luteum and therefore no progesterone. This is common in PCOS, hypothalamic amenorrhea, and perimenopause. Without the progesterone-induced transformation, the uterine lining may shed irregularly, causing unpredictable or heavy bleeding. Progesterone testing helps identify anovulatory cycles.
Polycystic Ovary Syndrome (PCOS)
Many women with PCOS have irregular or absent ovulation, resulting in low progesterone. The lack of regular progesterone exposure can lead to irregular periods and may increase risk of endometrial hyperplasia over time. Progesterone testing helps assess ovulatory status, and progesterone supplementation may be used to induce regular withdrawal bleeding.
Recurrent Pregnancy Loss
Some cases of recurrent miscarriage may relate to inadequate progesterone. While not all miscarriages are caused by low progesterone, evaluation of luteal function is part of the workup for recurrent loss. Progesterone supplementation is often prescribed empirically, though evidence of benefit is mixed.
Infertility
Progesterone testing is a standard component of infertility evaluation. It confirms whether ovulation is occurring and assesses luteal phase adequacy. Both anovulation and luteal phase deficiency are treatable causes of infertility. During fertility treatment, progesterone supplementation is routine to optimize implantation conditions.
Abnormal Uterine Bleeding
Irregular or heavy menstrual bleeding often relates to anovulation and resulting progesterone deficiency. Without progesterone to stabilize the endometrium after estrogen priming, the lining sheds unpredictably. Progesterone testing helps identify this pattern, and cyclic progesterone therapy can regulate bleeding.
Related Biomarkers Often Tested Together
Estradiol — Works with progesterone in the menstrual cycle; estradiol dominates the follicular phase, progesterone the luteal phase.
LH — The LH surge triggers ovulation and corpus luteum formation, which then produces progesterone.
FSH — Part of complete ovarian function assessment.
hCG — In early pregnancy, interpreted alongside progesterone to assess viability.
Prolactin — Elevated prolactin can cause anovulation and low progesterone.
Thyroid Panel — Thyroid dysfunction can affect ovulation and progesterone production.
Note: Information provided in this article is for educational purposes and doesn’t replace personalized medical advice.
Frequently Asked Questions
Progesterone is a hormone produced by the corpus luteum after ovulation. It prepares the uterine lining for pregnancy and supports early pregnancy. If pregnancy doesn’t occur, falling progesterone triggers menstruation.
For confirming ovulation, test about 7 days after ovulation — typically day 21 of a 28-day cycle. Adjust timing based on your cycle length: if your cycles are 35 days, ovulation is likely around day 21, so test around day 28.
It depends on timing. Low progesterone before ovulation is normal. Low progesterone in the mid-luteal phase suggests either no ovulation occurred or the corpus luteum isn’t producing adequately (luteal phase deficiency). Both situations can affect fertility.
Low progesterone is associated with miscarriage risk, but whether it causes miscarriage or is simply a marker of an already-failing pregnancy is debated. Progesterone supplementation is commonly prescribed in early pregnancy when levels are low, particularly after fertility treatment.
No. Elevated progesterone confirms ovulation occurred but doesn’t confirm pregnancy. Progesterone rises after every ovulation, whether or not pregnancy results. Pregnancy is confirmed by hCG testing.
Rarely. Men produce small amounts of progesterone, but testing is not routine. It may be checked in specific situations like suspected congenital adrenal hyperplasia or certain hormone-producing tumors.
Yes. Anovulatory cycles can still produce bleeding, though it’s technically “withdrawal bleeding” rather than true menstruation. Without ovulation, there’s no corpus luteum and no progesterone rise. Progesterone testing distinguishes ovulatory from anovulatory cycles.
References
Key Sources:
- Practice Committee of the American Society for Reproductive Medicine. Current clinical irrelevance of luteal phase deficiency: a committee opinion. Fertil Steril. 2015;103(4):e27-32.
- Coomarasamy A, et al. A randomized trial of progesterone in women with bleeding in early pregnancy. N Engl J Med. 2019;380(19):1815-1824.
- Practice Committee of the American Society for Reproductive Medicine. The clinical relevance of luteal phase deficiency: a committee opinion. Fertil Steril. 2021;115(6):1416-1423.
