Integrated Luteal Progesterone (ILPL)

Integrated luteal progesterone (ILPL) is a single number that combines how much progesterone a woman makes after ovulation with how long her luteal phase lasts. One blood test gives a snapshot. ILPL turns the whole phase into one value.

The reason to measure it that way is easy to see. Among 52 women with infertility, 13 had luteal phase deficiency confirmed on biopsy. Their integrated luteal progesterone was clearly lower than in the 39 with normal biopsies, while their mid-luteal progesterone did not differ.¹ Their luteal phase also ran shorter, averaging 11.0 days against 13.2.¹

The measure stays a research tool rather than a routine order. The lesson carries over. A short luteal phase and a normal single progesterone value can sit in the same cycle.