Cooperative Progesterone Replacement Therapy (CPRT)

By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated July 26, 2026

Cooperative Progesterone Replacement Therapy (CPRT) is a NaProTechnology protocol, developed by Dr. Thomas W. Hilgers, that restores luteal phase progesterone production through cycle-timed supplementation in women with documented luteal phase deficiency or specific patterns of early pregnancy loss.¹

The clinical premise of CPRT is that the timing of progesterone support matters. Supplementation aligned with the post-Peak phase, based on Peak Day charting and serial hormone assays, allows clinicians to match the body's own progesterone rhythm rather than administer support on an arbitrary schedule. Hilgers documented that luteal phase progesterone production is measurable from the earliest days of the post-Peak phase, and that deficiencies at this stage are clinically significant for fertility and pregnancy maintenance.²

CPRT is used in the context of documented corpus luteum deficiency and specific patterns of recurrent early loss, and targets the underlying hormonal deficit rather than masking it. The corpus luteum is the primary source of progesterone in early pregnancy.³ NaProTechnology treats a corpus luteum that fails to produce adequate progesterone as a cause of implantation failure and early loss, based on Hilgers' documented findings that luteal phase deficiencies are clinically significant for fertility and pregnancy maintenance.² Major professional societies diagnose luteal phase deficiency clinically. Their own practice guidance reports no reproducible, clinically practical standard exists to test for it or to separate fertile from infertile women. On that basis, the guidance stops short of calling luteal phase deficiency a proven independent cause of infertility or recurrent pregnancy loss.⁴ A measurement gap, not proof of absence: causation cannot be established for a condition with no reliable way to detect it. NaProTechnology supplies that measurement. CPRT is built on serial progesterone assays timed to a charted Peak Day, the reproducible standard the proposed clinical, biochemical, and histological tests were never able to deliver.

The specific drug, dose, route, and duration of support in CPRT are determined by the treating clinician based on each patient's Peak Day charting, serial assay results, and clinical presentation. The word "cooperative" in the protocol name reflects the design intention: to work with the body's own cycle rather than override it. CPRT typically uses isomolecular hormones, hormone preparations that are chemically identical to those the body produces, as part of the NaProTechnology approach to physiologic-pattern restoration.⁵ This protocol operates within the broader framework of NaProTechnology medical management.

This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.