Progesterone Levels During the Menstrual Cycle
Progesterone is at its lowest during the follicular phase of a woman's menstrual cycle, specifically during menstruation and the early follicular phase (days 1-7), with levels essentially equivalent to male baseline levels.
Timing of Lowest Progesterone Levels
Progesterone levels are minimal during the follicular phase, with research demonstrating that follicular-phase serum progesterone levels in nonsmoking women (21.4 ± 5.4 ng/dl) do not significantly differ from levels in men (18.1 ± 3.1 ng/dl), indicating essentially no ovarian progesterone secretion during this phase 1.
The follicular phase progesterone level averages 0.65 ± 0.12 ng/ml, which is 10-15 times lower than luteal phase levels (12.4 ± 2.3 ng/ml) 2.
Progesterone remains low from menstruation through ovulation, which typically occurs around days 9-20 of an average 28-day cycle 3.
Hormonal Pattern Throughout the Cycle
Follicular Phase (Days 1-14)
- Progesterone levels remain at baseline with minimal ovarian secretion 1.
- Ovulation separates the follicular and luteal phases, following a sharp increase in luteinizing hormone, estrogen, and follicle-stimulating hormone 3.
Luteal Phase (Post-Ovulation)
- Progesterone levels progressively increase during the luteal phase, reaching peak concentrations at the mid-luteal phase 3.
- Progesterone levels are highest during the luteal phase when progesterone levels are at their peak, which is clinically relevant for conditions like acute hepatic porphyrias where cyclic attacks occur during this high-progesterone period 3.
- Mid-luteal phase progesterone measurement (typically day 25-26 of the cycle) is used clinically to confirm ovulation, with levels <6 nmol/l indicating anovulation 3.
Clinical Implications
- A single serum progesterone level ≥5 ng/ml confirms ovulation with 98.4% specificity and 89.6% sensitivity 4.
- Progesterone secretion occurs in a pulsatile fashion during the luteal phase, leading to highly variable serum levels when samples are obtained at random 5.
- The general decrease in progesterone in the late luteal phase (approaching menstruation) is due to decreased progesterone pulse amplitude 5.