Long-time vs. short-time insemination of sibling eggs

This study aimed to evaluate the impact of a short insemination procedure on embryo development, assess the reliability of a fertilization check prior to the appearance of pronuclei and elucidate the role of rescue intracytoplasmic sperm injection (R-ICSI). Patients who had ≥9 eggs, were aged <38 years and had normal semen samples were included. The sibling eggs of each patient were divided into two groups; one half for conventional in vitro fertilization (IVF; insemination time, 20 h) and the other half for short insemination (insemination time, 5 h). R-ICSI was performed where total fertilization failure (TFF) was deemed to have occurred in the short insemination group. In total, 2,465 eggs were included. No significant differences were found in fertilization, abnormal fertilization, embryo quality, clinical pregnancy and implantation rates between the short insemination and conventional insemination groups. In the short insemination group, R-ICSI was performed in 11 cycles (6.7%); in 6 of these cycles, fertilization occurred in the patient's eggs in the 20 h insemination group, while in the other 5 cycles, the patient's eggs were not fertilized after 20 h insemination either. Following R-ICSI, 19 of 36 eggs were normally fertilized. Subsequently, 7 embryos were transferred in 4 fresh cycles resulting in one ectopic pregnancy. In conclusion, the short insemination procedure does not improve embryo development and pregnancy rates. Short insemination combined with early R-ICSI may be a method of preventing total fertilization failure, albeit with poor accuracy.