between the rCL and the non-rCL groups were analyzed, as appropriate, with t tests or Mann-Whitney U tests. P < 0.05 was considered statistically significant.Two women were excluded from the analysis because of corpus luteum persistence-as defined by serum progesterone levels of 2 ng/ mL or more on D1-before receiving rhCG. Rescued corpus luteum occurred in 19 (67.9%) of the remaining 28 participants, with the other 9 (32.1%) classified as having non-rCL. Serum progesterone and estradiol levels following rhCG administration were significantly greater in the rCL group than in the non-rCL group (P < 0.01; Table 1).Serum levels of FSH and LH did not differ significantly between the groups on D1 or D3.Rescued corpus luteum was observed in a surprisingly large proportion-approximately two-thirds-of women undergoing ovulation induction with a GnRH antagonist who received a single pharmacophysiologic dose of rhCG on D1. Although rCL was not a universal feature among women who were administered rhCG on D1, efforts to limit its occurrence should be made to prevent the possible harmful effects on IVF outcome of a premature increase in progesterone levels.