How does the short insemination method affect clinical outcomes and laboratory management?(第39回ヨーロッパ生殖医学会(ESHRE))
Yukino Matsuda, Shinichi Watanabe, Mari Tomida, Shigenori Suzuki, Kaori Yoshikai, Eiko Nakano, Tomio Sawada
Sawada Women’s Clinic, Nagoya, Japan

Study question
Does the short insemination method using a time-lapse monitoring system improve clinical outcomes and laboratory management?

Summary Answer
The method increased the normal fertilization rate of Conventional IVF and also increased the 3PN rate. The working environment of the laboratory staff was improved.

What is known already
Short insemination using a time-lapse monitoring system has been reported to reduce fertilization confirmation failures due to loss of pronuclei, but many reports indicate that the method was implemented to perform so-called 'rescue ICSI' for unfertilized oocytes on the day of egg retrieval and there are not many reports of clinical outcomes in conventional IVF without rescue ICSI. There are also few reports on the working environment and working hours in the laboratory.

This was a retrospective study of 3714 oocytes from 715 cycles in 595 patients who underwent Conventional IVF with egg retrieval in 2016-2022.
Long insemination (1577 oocytes) was performed in cycles up to May 2019 and short insemination (2137 oocytes) in later cycles.
In IVF, 40,000 motile sperm were placed in 1 ml of culture medium per oocyte.

Materials and Methods
Oocytes of the long insemination group (group L) were inseminated 5 hours after egg retrieval and denuded 19 hours later to observe their pronuclei.
Oocytes from the short insemination group (group S) were inseminated 2 hours after egg retrieval, denuded 4 hours later, and cultured in EmbryoScope (Vitrolife, Sweden) to observe the pronuclei.
Since the working hours set at our clinic are 8:00 A.m.-5:00 p.m., the time schedule for both groups followed this schedule.

The 2PN rate was 60.9% in group L and 64.7% in group S. The 3PN rates were 7.5% and 10.2% respectively, both rates being significantly higher in group S (P<0.05). The non-fertilization rates were significantly higher in group L (25.3% and 21.7% respectively); the 1PN rate was not significantly different (3.6% vs. 3.4%).
The rate of missed pronuclei was 2.8% in group L and 0% in group S.
Early embryo transfer pregnancy rate (25.4% vs 27.8%), good blastocyst development rate (52.2% vs 63.6%) and blastocyst transfer pregnancy rate (41.1% vs 31.7%) in groups L and S respectively.
The good blastocyst incidence was significantly higher in group S.
In the case of the Conventional IVF cycle in which egg retrieval was performed at 8:00 a.m., the embryologists in group L were to observe the pronuclei at 8:00 a.m. the next day, but in reality the embryologists had to come to work earlier because of denudation, and even then pronuclear loss occurred.
In contrast, the group S did not require an earlier attendance because denudation was not performed the next morning, and the time-lapse images did not fail to confirm the pronuclei at all.

Limitations, reasons for caution
Since the short insemination method was introduced at our clinic in June 2019, this study compared clinical outcomes before and after that date.

Wider implications of the findings
It has been reported in the past that early insemination time increases both 2PN and 3PN rates. The short insemination method in this study also used a faster insemination time, which may have led to similar insemination results.

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