Progesterone
HormonesAlso known as: P4, corpus luteum hormone
Progesterone is a hormone produced after ovulation and during pregnancy.
It plays a key role in regulating the menstrual cycle, preparing the uterus for pregnancy, and supporting early pregnancy. In non-pregnant women, progesterone drops trigger menstruation.
Why this matters
Progesterone levels reveal how well your reproductive system is functioning. Low progesterone can cause irregular periods, difficulty conceiving, or early pregnancy loss, while high levels outside pregnancy may indicate hormone imbalances or ovarian conditions. Maintaining a healthy lifestyle, managing stress, and working with a healthcare provider to monitor hormone levels helps support reproductive health and fertility.
How this connects to other biomarkers
- In women, day 21 (mid-luteal phase) Progesterone > 30 nmol/L confirms ovulation has occurred that cycle; persistently low values across the cycle suggest anovulation (failure to ovulate).
- Elevated Progesterone in non-pregnant, non-luteal samples can indicate adrenal sources or congenital adrenal hyperplasia (consider 17-OHP testing).
- Progesterone is a substrate for cortisol and aldosterone synthesis — chronic stress with elevated Cortisol can deplete progesterone ("pregnenolone steal").
How often should I test Progesterone?
In premenopausal women, draw progesterone in the mid-luteal phase (typically days 19 to 22 of a 28-day cycle). For postmenopausal women on cyclic HRT or men, yearly testing is appropriate. After starting or adjusting progesterone therapy, retest at 6 to 12 weeks.
At baseline / for screening: In premenopausal women, draw in the mid-luteal phase (typically days 19 to 22 of a 28-day cycle) to confirm ovulation. For postmenopausal women on cyclic HRT or men, once every 12 months as part of a hormone panel.
When monitoring an intervention or change: Retest 6 to 12 weeks after starting or adjusting hormone therapy (HRT, oral contraceptives, fertility medication). Cycle phase matters as much as cadence, so match the cycle day across draws for meaningful comparison. In perimenopause, expect significant cycle-to-cycle variability that settles only after menopause is established.
Note: Outside the mid-luteal window, low progesterone reflects cycle phase rather than deficiency. Track in the mid-luteal phase (days 19 to 22 of a 28-day cycle), or use postmenopausal or cycle-suppressed baselines for stable comparisons.
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