Progesterone
Also known as: P4
What Does Progesterone Measure?
Progesterone (P4) is a steroid hormone primarily produced by the corpus luteum in the ovaries after ovulation, as well as by the placenta during pregnancy and in smaller amounts by the adrenal glands. A blood test measuring progesterone quantifies the concentration of this hormone circulating in the bloodstream, typically expressed in nanograms per milliliter (ng/mL) or nanomoles per liter (nmol/L). In women, levels fluctuate dramatically throughout the menstrual cycle, rising sharply after ovulation and falling if pregnancy does not occur. In men, progesterone is produced in small amounts by the adrenal glands and testes, where it serves as a precursor to other hormones.
Why Does Progesterone Matter?
Progesterone plays a central role in reproductive health, particularly in preparing the uterine lining (endometrium) for embryo implantation and maintaining early pregnancy. Adequate progesterone levels are essential for preventing miscarriage, regulating the menstrual cycle, and balancing the effects of estrogen. Beyond reproduction, progesterone influences mood, sleep quality, bone density, thyroid function, and the immune system. Low progesterone is one of the most common hormonal imbalances in women and can contribute to infertility, irregular periods, PMS, and increased risk of certain cancers. Monitoring progesterone levels helps clinicians diagnose ovulation disorders, assess pregnancy viability, investigate infertility, and guide hormone replacement therapy.
Normal Ranges
Males
0.2–1.4 ng/mL (0.6–4.5 nmol/L)
Females
Follicular phase: 0.1–0.9 ng/mL; Ovulatory phase: 1.8–24.0 ng/mL; Luteal phase: 1.7–27.0 ng/mL; Postmenopausal: <0.1–0.8 ng/mL; Pregnancy (1st trimester): 11–44 ng/mL
Children
Prepubertal: <0.1–0.5 ng/mL; varies by age and pubertal stage
Causes of High Levels
- Pregnancy (placenta produces large amounts, especially in 2nd and 3rd trimesters)
- Ovarian cysts, particularly luteal cysts that continue secreting progesterone
- Congenital adrenal hyperplasia (CAH), where adrenal enzyme defects cause progesterone accumulation
- Ovarian or adrenal tumors producing excess progesterone
- Exogenous progesterone use (supplements, birth control, hormone replacement therapy)
- Molar pregnancy or other gestational trophoblastic diseases
Causes of Low Levels
- Anovulation (failure to ovulate), meaning no corpus luteum forms to produce progesterone
- Luteal phase defect, where the corpus luteum doesn't produce adequate progesterone after ovulation
- Polycystic ovary syndrome (PCOS), which disrupts regular ovulation
How to Improve Your Progesterone
Diet
- Increase consumption of zinc-rich foods (pumpkin seeds, beef, shellfish) to support corpus luteum function and progesterone synthesis
- Eat foods high in vitamin B6 (chickpeas, salmon, bananas, poultry) as B6 is essential for progesterone production and reducing excess estrogen
- Include magnesium-rich foods (dark leafy greens, nuts, seeds, dark chocolate) to support adrenal function and reduce cortisol that suppresses progesterone
- Consume adequate healthy fats (avocados, olive oil, nuts, fatty fish) as cholesterol is the building block for all steroid hormones including progesterone
- Reduce refined sugars and processed carbohydrates to stabilize insulin levels, as insulin resistance can disrupt ovulation and hormone production
Supplements
- Vitex (Chasteberry) 400–500 mg daily — an herbal supplement that may support the pituitary gland to stimulate progesterone production; results seen after 3–6 months
- Vitamin B6 50–100 mg daily to support luteal phase function and progesterone levels
- Magnesium glycinate 200–400 mg daily to reduce cortisol and support hormone balance
- Zinc 25–30 mg daily with food to promote ovulation and support corpus luteum function
Related Biomarkers
Frequently Asked Questions
When should progesterone be tested during the menstrual cycle?
Progesterone is most informative when tested during the mid-luteal phase, approximately 7 days after ovulation (or around day 21 of a 28-day cycle). This is when progesterone peaks if ovulation has occurred. Testing at other times can be misleading because levels are naturally very low during the follicular phase. If your cycle is irregular, your doctor may time the test based on tracking ovulation signs or may order serial tests.
What is a 'good' progesterone level to confirm ovulation?
A mid-luteal progesterone level above 3 ng/mL (10 nmol/L) is generally considered evidence that ovulation has occurred. However, many fertility specialists prefer to see levels above 10 ng/mL to confirm adequate corpus luteum function. Levels between 1.7–27 ng/mL are considered normal for the luteal phase, but your doctor will interpret your result in the context of your cycle day, symptoms, and fertility goals.
Can low progesterone cause miscarriage?
Low progesterone in early pregnancy is associated with an increased risk of miscarriage, as progesterone is essential for maintaining the uterine lining and supporting the developing embryo. However, it is often debated whether low progesterone causes miscarriage or is itself a symptom of a pregnancy that was already failing. Some studies support the use of progesterone supplementation in early pregnancy for women with a history of recurrent miscarriage and low levels, and this is increasingly offered as a precautionary treatment.