Short insemination during conventional in vitro fertilization increases embryo quality.

Aim: To compare clinical outcomes using short and long co-incubation protocols in sibling oocytes based on embryo morphokinetic outcomes measured by time-lapse incubator with stratification based on a woman's age and sperm quality.

Design: Our study included 72 cycles with >6 oocytes retrieved. Sibling oocytes were distributed for two parallel protocols: short (3 h; n = 421) or long (16-20 h; n = 434) insemination, using the same amount of spermatozoa from the same prepared sample. Oocytes were then washed and incubated for 5 days. Time-lapse annotations of embryos were performed by experienced embryologists and artificial intelligence-based Known Implantation Data scores for day 3 and day 5 were calculated with EmbryoScope software.

Results: Short-insemination group exhibited a higher blastulation rate, better morphokinetic indicators, and higher Known Implantation Data scores on day 3 and day 5 of the utilized embryos. However, the fertilization rate and clinical pregnancy rate per embryo transfer did not differ between experimental groups. A higher rate of abnormal fertilization (>2 pronuclei) after long insemination was recorded in women under 35 years old or with a total motile sperm count above 5 million and above 40% motility after preparation. A higher rate of usable embryos was observed after short insemination with a total motile sperm count above 30 million before preparation or 5 million and over 40% motility after preparation.

Conclusions: Our results suggest that a short insemination protocol results in better embryo quality and should be considered as a favorable protocol, especially in young female patients or male patients with high sperm quality.