Hum. Reprod. Advance Access originally published online on January 29, 2004
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Human Reproduction, Vol. 19, No. 3, 573-578,
March 2004
© 2004 European Society of Human Reproduction and Embryology
Laser-assisted zona pellucida thinning prior to routine ICSI
Women’s General Hospital, IVF Unit, Lederergasse 47, A-4010 Linz, Upper Austria, Austria
1 To whom correspondence should be addressed. e-mail: Marianne.moser{at}gespag.at
BACKGROUND: In MII oocytes showing difficult oolemma breakage, ICSI can cause an increase in the degeneration rate. This may be overcome by laser-assisted ICSI using a 5–10 µm opening in the zona pellucida for injection. However, such a small opening might impair the hatching process, especially if assisted hatching is applied in addition. In order to prevent this, the present study used routine injection through an area of zona pellucida in which laser zona thinning had been applied, providing for both a reduced mechanical stress to the oocyte and assisted hatching. METHODS: This prospective study involved 100 cycles with 1016 MII oocytes. Conventional ICSI (control group) was compared with a modified laser-assisted ICSI (study group) in sibling oocytes. In the latter group oocytes were injected through an extended area of zona thinning. RESULTS: Degeneration rate was significantly lower in the study group (P < 0.004). There were no differences in fertilization, or formation and quality of blastocysts. In the study group embryo quality on day 2 was significantly better (P = 0.004) and herniation of day 5 blastocysts was increased (P = 0.005). Rates of implantation and pregnancy were not affected. However, on day 3 laser-assisted ICSI proved beneficial (P = 0.038) in terms of clinical pregnancy rate. CONCLUSIONS: The new method combines a less invasive ICSI technique with assisted hatching. Our preliminary data indicate that in addition to an improved oocyte survival, this new approach increases the hatching rate in vitro, which may explain the increase in pregnancy rate, at least in day 3 transfers.
Key words: assisted hatching/blastocyst stage/laser assisted ICSI/oocyte survival/zona pellucida thinning
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