P-130 Comparing head-first and tail-first injection techniques in guiding new embryologists for human oocyte Piezo-ICSI
Authors: Hiraoka K , Uchida N , Nakajo H , Sato M , Osugi M , Sujino T , Komiya A , Katsumata S , Takayanagi Y , Nako Y , Tajima M , Kawai K 
Published: July 2024

Abstract

Study question
Which technique is more effective for new embryologists in human oocyte Piezo-ICSI: Head-first or tail-first injection?

Summary answer
Tail-first injection is superior as it significantly increases fertilization rates without adversely affecting embryo development compared to head-first injection in Piezo-ICSI.

What is known already
ICSI is an essential technique in assisted reproductive technology. Recently, some researchers have reported that Piezo-ICSI is clinically more useful than Standard-ICSI. In most papers, Piezo-ICSI has shown significantly higher fertilization rates than Standard-ICSI. This is because, in Piezo-ICSI, it eliminates the need to aspirate the cytoplasm into the ICSI needle upon membrane breakage. After membrane breakage, the sperm is injected into the cytoplasm. A few papers evaluated the effect of sperm injection direction (head-first or tail-first) on ICSI results for human oocytes. However, little information is available to guide new embryologists on whether to use head-first or tail-first injection.

Study design, size, duration
During their Piezo-ICSI training, new embryologists were taught either head-first or tail-first injection techniques before commencing clinical procedures. Only the head part of the sperm was injected into the cytoplasm in the head-first group, and half of the whole sperm was injected in the tail-first group. This study divided the new embryologists into two groups (head-first or tail-first) and collected and retrospectively analyzed their first 200 oocyte ICSI results between January 2017 and November 2023.

Participants/materials, setting, methods
This study involved five new embryologists and a total of 1,000 oocytes. Two embryologists performed head-first injection for 400 oocytes, and three performed tail-first injection for 600 oocytes. The rates of degeneration, 2PN, 0PN, 1PN, ≥3PN, good quality day-3 embryo (≥7cell, ≤15%fragmemtation) per 2PN, blastocyst, and good quality blastocyst (better than BB with Gardner criteria) were compared. Statistical analysis was performed using either a t-test, Welch’s t-test, or Fisher’s exact test as appropriate.

Main results and the role of chance
The average ages of women and their husbands in the head-first and tail-first injection groups were 37.8 vs. 37.2 and 40.1 vs. 39.2, respectively, with average total motile sperm counts of 52.2 x106 vs. 52.6 x106. No significant difference was observed in these comparison items between the groups. Theoretical injected medium volume into the cytoplasm with sperm of the head-first and tail-first injection groups was 104μm3 vs. 520μm3. The 2PN rate of the tail-first injection group (88.3%; 530/600) was significantly higher (P = 0.0151) than head-first (82.8%; 331/400). The 0PN rate of the tail-first group (4.0%; 24/600) was significantly lower (P = 0.0007) than the head-first (9.5%; 38/400). The degeneration rates, 1PN rates, and ≥3PN rates of head-first and tail-first injection groups were 1.5% (6/400) vs. 1.3% (8/600), 3.5% (14/400) vs. 2.3% (14/600), and 2.8% (11/400) vs. 4.0% (24/600). No significant difference was observed in these comparison items between the groups. The good quality day-3 embryo per 2PN rates, blastocyst rates, and good quality blastocyst rates of head-first and tail-first injection groups were 64.7% (214/331) vs. 64.3% (341/530), 62.1% (192/309) vs. 62.7% (289/461), 35.3% (109/309) vs. 35.6% (164/461). No significant difference was observed in these comparison items between the groups.

Limitations, reasons for caution
The estimated volumes of medium injected into the cytoplasm for both head-first and tail-first injections were theoretical. We calculated the length of the sperm head and whole sperm as 6μm and 60μm. Some day-3 embryos were transferred or cryopreserved, so the blastocyst and good-quality blastocyst rates were reference ranges.

Wider implications of the findings
Despite the larger volume of medium injected with sperm, tail-first injection increases fertilization rates without adversely impacting embryo development compared to head-first injection. Therefore, the tail-first injection is better to guide the new embryologists for human oocytes Piezo-ICSI than the head-first injection.

Trial registration number
17-0450221102