Elevated progesterone levels on the day of trigger negatively impact the outcome of assisted reproductive technique (ART) treatment and forced ovarian stimulation might be a cause of progesterone elevation during ovarian stimulation. To analyze the impact of forced and prolonged stimulation on the progesterone elevation, this data analysis from the Ensure study compared hormonal stimulation with corifollitropin alpha (CFA)-only with CFA plus recombinant (rec) follicle-stimulating hormone (FSH) after day 8 (CFA-plus group) of ovarian stimulation. In the Ensure study, 268 patients underwent ovarian stimulation with 100 mg CFA and 128 patients with recombinant FSH. A total of 35 patients (13.1%) from the CFA-arm received the hCG trigger after stimulation with CFA-only, 233 patients (86.9%) needed additional rec FSH from day 8 onwards to meet the criteria for trigger. Progesterone levels >0.8 ng/ml on the trigger day occurred in 90 patients (38.6%) from the CFA plus FSH group and only in one patient (2.8%) in the CFA-only group (p < .001). The ongoing pregnancy rate (OPR) was 31.4% (11/35) for patients in the CFA-only group and 24.5% (57/233) for patients CFA-plus group with additional recFSH after day 8 (p1⁄4 .378). This set of data demonstrates that prolongation of stimulation in combination with intense stimulation leads to a statistically significant increased incidence of progesterone elevation on the day of trigger.