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We aimed to answer one key question, that was not previously addressed as to whether serum progesterone (P4-hCG day) and its co-variates (estradiol (E2-hCG day) and the number of retrieved oocytes) of a given cycle can be predictive of the subsequent cycle when both cycles are consecutive and comparable for the stimulation protocol, gonadotropin dose and duration of stimulation. We analyzed such 244 consecutive (< 6 months) IVF cycles in 122 patients with GnRH agonist long protocol and found that P4, E2 and the number of retrieved oocytes significantly vary between the two cycles. Although P4 increased (ranging from 4.7 to 266.7%) in the 2nd cycle in 61 patients, E2 and the number of retrieved oocytes, which are normally positively correlated with P4 paradoxically decreased in the 41% and 37.7% respectively, of these same 61 patients. When a similar analysis was done in the 54 out of 122 patients (44.3%) in whom serum P4 was decreased in the 2nd cycle, the mean decrease in P4 was − 34.1 ± 23.3% ranging from − 5.26 to − 90.1%. E2 and the number of retrieved oocytes paradoxically increased in the 42.3% and 40.7% of these 54 patients respectively. P4 remained the same only in the 7 (5.7%) of these 122 patients. These findings indicate that late follicular phase serum P4 may change unpredictably in the subsequent IVF cycle. The changes are not always necessarily proportional with ovarian response of previous cycle suggesting that growth characteristics and steroidogenic activities of antral cohorts may exhibit considerable cycle to cycle variations. [ABSTRACT FROM AUTHOR]