Clinical Outcomes of Rescue Intracytoplasmic Sperm Injection at Different Timings Following In Vitro Fertilization

Yuki Shiraiwa, Noritoshi Enatsu, Kazuki Yamagami, Koyu Furuhashi, Toshiroh Iwasaki, Junko Otsuki, Masahide Shiotani

Research output: Contribution to journalArticlepeer-review


Background: Although rescue intracytoplasmic sperm injection (r-ICSI) is extensively used worldwide, the indication of r-ICSI and its optimal timing remains obscure. This study aimed to assess the outcomes of r-ICSI following in vitro fertilization in different timings when fertilization is confirmed. Methods: This study included 5,156 cycles (47,785 eggs). Fertilization was confirmed by polar body analysis after 4 and 6 hr of coincubation of the sperm and oocyte. Oocytes that underwent IVF were divided into two groups based on the time when a second polar body was detected in more than 30% of all oocytes (Four-hr group and six-hr group). If the second polar body was not detected or was present in less than 30% of all oocytes after six hr of coincubation, rescue-ICSI (r-ICSI) was performed for oocytes without a second polar body (r-ICSI group). Results: The fertilization rates of two pronuclear (2PN) oocytes in the three groups (Four-hr group, six-hr group, and r-ICSI group) were 70.7%, 51.3%, and 58.0%, respectively. The blastocyst formation rates were 62.8%, 53.4%, and 42.9%, respectively. Conclusion: Performing r-ICSI after six hr of coincubation can salvage cases with fertilization failure in IVF. The higher fertilization rate of r-ICSI indicates that all oocytes without signs of fertilization after six hr of coincubation should undergo r- ICSI.

Original languageEnglish
Pages (from-to)251-257
Number of pages7
JournalJournal of Reproduction and Infertility
Issue number4
Publication statusPublished - Oct 2021


  • Assisted reproductive techniques
  • Fertilization failure
  • In vitro fertilization
  • Infertility
  • Intracytoplasmic sperm injection

ASJC Scopus subject areas

  • Reproductive Medicine


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