How will I know what my luteal phase is without information?

Test and Question. You need some information to understand the luteal phase. You can check the number of days after ovulation, measure Progesterone (p4) levels, or biopsy the endometrium to indirectly see the effect of p4. Luteal phase defect (lpd) implies a low p4 after ovulation. The diagnosis is controversial because measuring p4 is easy but interpreting the results is tricky.