Characterization of the normal progesterone and placental protein 14 responses to human chorionic gonadotropin stimulation in the luteal phase

Objective: To examine whether midluteal phase administration of the luteotrophic hormone hCG can result in higher and more stable serum levels than random sampling of P and placental protein 14 (PP14). Design: Prospective controlled clinical study. Setting: Normal human volunteers in an academic research environment. Participants: Twenty-six fertile, regularly cycling women. Interventions: Blood samples were drawn at 0, 3, 6, 9, 12, 18, and 24 hours and then daily for the next 6 days, after a single IM injection of 5,000 IU hCG or saline given on day 5, 7, or 9 after the LH surge, as detected by rapid plasma assays. Main Outcome Measures: Serum P and PP14 measurements. Results: Peak P and PP14 concentrations occurred at 6 hours and 5 days, respectively, after hCG stimulation on luteal phase day 9. Progesterone but not PP14 levels were significantly higher and less variable after hCG than after saline administration on this day. Progesterone responses exceeded 11.0 ng/mL (35.0 nmol/L) in all women, suggesting that this represents the cutoff limit for normal luteal function. Because PP14 responses were highly variable and inconsistent, it was not possible to determine a threshold for normal endometrial function. Conclusions: Midluteal phase administration of hCG in normal women induces consistent serum P levels > 11.0 ng/ml (35.0 nmol/L) but highly variable PP14 responses.