Delayed fertilization during in vitro fertilization and embryo transfer cycles: Analysis of causes and impact on overall results

This study evaluated possible causes of delayed fertilization during in vitro fertilization (IVF) cycles, its repetitiveness, and its influence on IVF results in 23 patients (27 cycles) with delayed fertilization of ≥1 preovulatory oocyte(s). In 15 cycles, reinsemination with husband's semen was performed at 18 hours. Possible causes of delayed fertilization were oocyte defects (10 cycles, 37.0%), sperm defects (4 cycles, 14.8%), oocyte and sperm defects (4 cycles, 14.8%), and no detectable gamete defects (9 cycles, 33.3%). Overall fertilization rate was 47.9%. No pregnancies were observed in 10 patients with one embryo transferred. Recurrence rate of delayed fertilization per patient was 17.3%; overall ongoing pregnancy rate/cycle was 10.3%. Although repetitiveness of delayed fertilization is low, it seems to impact negatively on IVF results.