Cooperative Progesterone Replacement Therapy (CPRT)

Cooperative Progesterone Replacement Therapy (CPRT) is a NaProTechnology protocol that restores progesterone after ovulation. This part of the cycle is the luteal phase. Dr. Thomas W. Hilgers developed the protocol. It provides hormone support timed to the cycle. It is intended for women with documented luteal phase deficiency or certain patterns of early pregnancy loss.¹

CPRT rests on one principle: timing matters. Clinicians time support to the days after Peak. The timing comes from Peak Day charting and serial assays, which are repeated hormone blood tests. This approach allows clinicians to match the natural hormone rhythm of the body. They do not give support on an arbitrary schedule.

Hilgers showed that the body's own luteal progesterone can be measured from the first days of the post-Peak phase. He also found that low levels at this stage matter for fertility and for sustaining a pregnancy.²

CPRT is used for documented corpus luteum deficiency and certain patterns of repeated early loss. It targets the hormone deficit itself and does not mask it. The corpus luteum is the main source of progesterone in early pregnancy.³

A corpus luteum can produce too little progesterone. NaProTechnology regards that deficit as a cause of failed implantation and early loss. This position rests on the findings of Hilgers that low luteal levels matter for fertility and for sustaining a pregnancy.²

Major professional societies diagnose luteal phase deficiency by clinical judgment. Their own guidance reports that no reproducible, practical standard exists to test for it or to distinguish fertile from infertile women. For this reason, the guidance stops short of naming it a proven, stand-alone cause of infertility or repeated loss.⁴

This is a gap in measurement, not proof that the problem is absent. No one can prove a cause for a condition that cannot be reliably detected. NaProTechnology supplies that measurement. CPRT is built on repeated hormone tests timed to a charted Peak Day. The proposed clinical, blood, and tissue tests never produced a reproducible standard. Charted testing does.

The treating clinician selects the drug, dose, route, and duration of support. Each choice rests on the Peak Day chart, test results, and symptoms of the individual woman. The word "cooperative" in the name states the goal: to work with the natural cycle of the body rather than override it.

CPRT usually uses isomolecular hormones. These hormones match the hormones the body produces, down to the molecule. They are part of the NaProTechnology approach to restoring the natural hormone pattern of the body.⁵ CPRT sits within the wider framework of NaProTechnology medical care.