I noticed that some patients have progesterone changes around ovulation, before the corpus luteum has formed. Why is that?Updated 2 months ago

A rise in progesterone occurs in the hours before and during the LH surge due to early luteinization of granulosa and theca cells. The LH surge triggers several simultaneous processes:

1. LH receptor signaling stimulates the granulosa cells to begin expressing the enzymes needed for progesterone synthesis, including P450scc and 3β-HSD.
2. Increased progesterone production by granulosa cells occurs even before ovulation is complete, as these cells begin their conversion from follicular to luteal phenotype.
3. Pre-ovulatory progesterone from the dominant follicle contributes to the coordinated hormonal events that precede and enable ovulation.

This pre-ovulatory progesterone rise is physiologically normal, and it reflects the beginning of luteinization, not an artifact or pathology. The much larger rise in progesterone occurs over the subsequent 7–10 days as the mature corpus luteum develops.

References:

• Baird DT, Uno S, et al. "The secretion of immunoreactive luteinizing hormone and follicle-stimulating hormone during the normal menstrual cycle." Clinical Endocrinology, 1976.
• Erickson GF. "The ovarian follicle: structure and function in reproductive physiology." Endocrine Reviews, 1978.
• Stricker R, et al. "Establishment of detailed reference values for luteinizing hormone, follicle-stimulating hormone, estradiol, and progesterone during different phases of the menstrual cycle on the Abbott ARCHITECT analyzer." Clinical Chemistry and Laboratory Medicine, 2006.