P-208 Effect of direction of sperm injection (head-first or tail-first) in Piezo-ICSI on single embryo transfer and perinatal outcomes: data from 3,021 transfers and 931 infants

Study question Does tail-first injection in human Piezo-ICSI affect single embryo transfer and perinatal outcomes compared with head-first injection? Summary answer Tail-first injection in human Piezo-ICSI does not have an adverse effect on single embryo transfer and perinatal outcomes compared with head-first injection. What is known already ICSI is a crucial technique in human ART. Recently, some researchers have indicated that Piezo-ICSI is clinically more effective than Standard-ICSI. In most studies, Piezo-ICSI has demonstrated significantly higher fertilization rates than Standard-ICSI. Piezo-ICSI removes the need to aspirate cytoplasm into the ICSI needle at membrane breakage. Following membrane breakage, sperm is injected into the cytoplasm. A few studies have assessed the effect of sperm injection direction (head-first or tail-first) on ICSI outcomes for human oocytes. However, there is limited information about the impact of sperm injection direction (head-first or tail-first) in Piezo-ICSI on single embryo transfer and perinatal outcomes. Study design, size, duration This retrospective study included 3,021 single embryo transfer cycles from 1,230 patients treated at two centers between June 2016 and December 2023. Among these, 1,344 single embryo transfer cycles involving 540 patients with head-first injection embryos and 1,677 cycles involving 690 patients with tail-first injection embryos. Nine hundred thirty-one infants were born from 918 deliveries, including 418 infants from 411 deliveries of head-first injection embryos and 513 infants from 507 deliveries of tail-first injection embryos. Participants/materials, setting, methods Single embryo transfer included cleaved embryos and blastocysts. The embryos from head-first and tail-first injections were compared, along with the women’s ages at oocyte pick-up and embryo transfer, pregnancy rates, delivery rates, monozygotic twin rates, sex ratio, infant birth weight, gestational weeks, and birth defect rates following the single embryo transfer. 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 ratio of single-cleaved embryo transfer cycles of head-first and tail-first injections was 10.9% (146/1344) and 16.5% (276/1677), and the ratio of blastocyst transfer cycles was 89.1% (1198/1344) and 83.5% (1401/1677), respectively. A significant difference was observed between the ratio of single-cleaved embryo transfer and blastocyst transfer cycles between the head-first and tail-first injections. Among the head-first and tail-first injections embryos transfer cycles, there were no significant differences when comparing the average number of the previous oocyte pick up (1.7±0.1 vs. 1.7±0.0), the average number of previous embryo transfer cycles (2.1±0.1 vs. 2.1±0.1), the average age of women at oocyte pick up (36.2±0.1 vs. 36.4±0.1), the average age of women at embryo transfer (36.8±0.1 vs. 36.9±0.1), pregnancy rates (40.8%; 548/1344 vs. 40.0%; 671/1677), delivery rates (30.6%; 411/1344 vs. 30.2%; 507/1677), monozygotic twin pregnancy rates (1.3%; 7/548 vs. 0.9%; 6/671), sex ratio (50:50 vs. 46:54), birth weight (2984±26.95 vs. 2982±23.98g), gestational week (38.2±0.2 vs. 38.2±0.1), and birth defect rates (1.2%; 5/418 vs. 1.2%; 6/513). Limitations, reasons for caution Although the ratio of single-cleaved embryo transfer cycles for head-first and tail-first injections differed significantly, we combined the data with blastocyst transfer data because the pregnancy and delivery rates of single-cleaved embryo transfer for head-first and tail-first injections were similar. Wider implications of the findings When fertilization occurs via IVF or ICSI, it is unclear whether the sperm’s tail takes part in the cytoplasm. Our results demonstrated for the first time that if the sperm’s tail is completely taking part in the cytoplasm, there is no adverse effect on embryo transfer and perinatal outcomes. Trial registration number No