研究開発・学会発表

Study question
This study aimed to determine if age affects the efficacy of piezo-assisted ICSI compared with conventional ICSI.

Summary answer
On day 6 in women older than 42 years old, the rate of blastocyst formation with piezo-assisted ICSI is significantly higher than that with conventional ICSI.

What is known already
Piezo-ICSI can achieve better fertilization and survival rates of fragile eggs compared with conventional ICSI because injury of oocytes is decreased as much as possible in piezo-ICSI. Generally, the fertilization rate of eggs depends on the age of women because eggs in older women are more fragile than those in younger women. However, there are few studies regarding appropriate indications for this method.

Study design, size, duration
A total of 847 mature oocytes from 98 cycles were used for this study from October 2013 to August 2014. At least four oocytes were retrieved from one cycle. Retrieved oocytes were divided into two groups: half of the oocytes underwent piezo-ICSI and the other half underwent conventional ICSI.

Participants/materials, setting, methods
Confirmation of fertilization in eggs was performed the next day, and then eggs were observed and graded on days 2, 5, and 6. Percentages of fertilization, degeneration after ICSI, good embryos, blastocysts, and good blastocysts were evaluated. Results were analyzed by age using the chi-square method.

Main results and the role of chance
Conventional ICSI and piezo-ICSI were used in 428 eggs and 419 eggs, respectively. The age of women ranged from 38 to 45 years old. When we analyzed the total number of embryos, there was no significant difference in percentages of results between the conventional group and the piezo-ICSI group. However, when we analyzed the results by age (38, 39, 40, 41, and older than 42 years old), women who were aged 42 years old or older had a significantly higher rate of blastocyst formation in the piezo-ICSI group compared with the conventional ICSI group (60.9% vs 25.0%, p=0.04). The rate of blastocyst formation was similar between the two groups for the other ages.

Limitations, reasons for caution
A limitation of this study was the inability to adopt our results to all women because of the small number of eggs included for each age, despite the considerable total number of eggs. A further, larger study is required to confirm our results.

Wider implications of the findings
This study partially clarified the indication for piezo-ICSI according to age compared with conventional ICSI. Based on our results, piezo-ICSI is recommended for older women (>42 years old) rather than younger women. Clinical trials, including clinical pregnancy and birth rates, are needed in the future to obtain more clear indications.