Despite recent improvements in equine ovum pick-up (OPU) combined with intracytoplasmic sperm injection (ICSI), there is still significant inter-individual variability. In this study, serum concentrations of the oocyte-secreted factors, growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15), as well as GDF9/BMP15 complex, anti-Müllerian hormone (AMH), progesterone (P4), and free and conjugated estradiol-17β (E2), were determined in 59 mares (3-24 years) at the time of OPU. Mares were classified retrospectively, based on the number of embryos obtained, into low or high outcome groups, using 2 or 3 embryos as the threshold values. Results of OPU-ICSI were not affected by the mare's age or body condition score, nor by the number of aspirated follicles, recovered oocytes, or the recovery rate (P > 0.05 in all cases). Mares with < 2 or ≥ 2 embryos had similar hormone levels (P > 0.05 in all cases), but there was a >90% likelihood of obtaining ≥ 2 embryos per session when P4 and E2 concentration was considered simultaneously. Mares with ≥ 3 embryos/session had lower P4 and higher AMH (P < 0.05 in both cases). GDF9 and BMP15 were detectable in 14% and 12% of mares, respectively, while GDF9/BMP15 complex was detected in 93% of mares, with no correlation to other factors. In conclusion, these preliminary findings suggest a negative correlation between high P4 levels and OPU-ICSI outcome in horses.