Regarding ovarian stimulation and embryological data, patients who developed severe early OHSS had lower total FSH dose (p = 0.014), higher number of follicles (p < 0.001) and higher oestradiol levels (p < 0.001) on the day of triggering final oocyte maturation, higher number of oocytes retrieved (p < 0.001), higher number of mature oocytes (p < 0.001), and higher number of fertilized oocytes (p < 0.001) compared to patients who did not develop severe early OHSS (Table3). This evidence concerns the gene BRD2 and ovarian hyperstimulation syndrome.