Mid‑Luteal Phase Progesterone Assessment Guidelines

Diagnostic Thresholds

• A mid‑luteal serum progesterone concentration below 6 nmol/L (≈2 ng/mL) defines anovulation, indicating that ovulation did not occur in the cycle evaluated. 1
• A single mid‑luteal progesterone value ≥30 nmol/L (≈9.4 ng/mL) confirms that ovulation has taken place; values between 6 nmol/L and 30 nmol/L fall into a gray zone that requires additional clinical correlation. 1

Timing of Measurement

• For optimal diagnostic accuracy, blood should be drawn in the mid‑luteal phase, roughly 7 days after ovulation (approximately cycle day 21 in a standard 28‑day cycle). This timing captures the peak luteal progesterone surge. 1

Assay and Laboratory Considerations

• Inter‑laboratory assay variability can affect absolute progesterone values, so clinicians should interpret results in the context of the specific assay’s reference range. 1

Physiological Variability

• Progesterone concentrations fluctuate throughout the luteal phase, meaning a single measurement reflects only a snapshot of ovarian function and may not represent the true peak level. 4