Is measurement of progesterone level prior to FSH stimulation useful in GnRH-antagonist cycles?

To reduce patient inconvenience during in vitro fertilization (IVF) cycles, some protocols delay intensive monitoring until mid-follicular stimulation. Others assess hormone levels prior to follicle-stimulating hormone (FSH) administration, not commencing stimulation until baseline progesterone (P4) levels (5 nmol/l) are achieved. Higher P4 levels (4.8 nmol/L) on the day of FSH trigger have been implicated in poorer pregnancy rates. This study evaluates the association of P4 levels at day 1-2 in gonadotrophin-releasing hormone (GnRH)-antagonist cycles with pre-trigger P4 levels and clinical pregnancy rates (CPRs).All fresh GnRH-antagonist IVF cycles between June 2011 and June 2012, in which pre-FSH P4 levels were not routinely performed (group 1), were retrieved from the IVF Australia database and compared with controls (group 2).There were 163 cycles in each group. P4 levels on the day of trigger were significantly higher in group 1 (3.75 vs. 2.77, p0.05). The incidence of pre-trigger P4 levels4.8 nmol/l was significantly higher in group 1 (30 vs. 16, p0.05). The number of oocytes retrieved was higher in group 1 (11.1 vs. 9, p0.05), however fertilization rates were significantly lower in that group (53.6% vs. 61.2%, p0.05); CPRs were similar between the two groups (27.8% vs. 31.8%, p = ns). Overall, pregnancy rates were lower in cycles with pre-trigger P4 level of4.8 nmol/L compared with those with lower levels (15% vs. 32.5%, p0.05).We found that measurement of P4 level at early follicular phase was associated with significantly lower pre-trigger levels. However, this did not translate into a difference in CPR between the monitored and unmonitored groups. We have confirmed that elevation in pre-trigger P4 level is associated with halving of the CPR, indicating that the most important P4 measurements are those in the late follicular/pre-trigger phase.