Luteal phase defect is best diagnosed by:

In luteal phase defect (LPD) as the name suggests there is decreased progesterone secretion which leads to premenstrual spotting and recurrent 1st trimester abortions Best method of diagnosing – LPD is endometrial biopsy done on day 21 day 23 of cycle (a lag of 48 hrs or more between the chronological dating and histological dating is diagnostic of LPD). It can also be diagnosed by serum progesterone levels– If serum progesterone done on day 21 of the cycle is < 5ng/ml-it indicates LPD.