Human Reproduction, Vol. 14, No. 10, 2677,
October 1999
© 1999 European Society of Human Reproduction and Embryology
Letters to the editor |
Normal development of a zona-free oocyte to the blastocyst stage following ICSI
The Institute of Advanced Medical Technology, 3154, Yakushiji, Minami-Kawachi, Kawachi, Tochigi, 329-0431, Japan
Dear Sir,
Recently, we were amazed to find an article (Ding et al., 1999
) which stated that zona-free blastocysts could be saved with intracytoplasmic sperm injection (ICSI). Just a week previous to reading their paper we performed a similar procedure with the same results. Most interesting is the similarity in our pictures (Figures 1 and 2).
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A 31 year old woman underwent ICSI because of male factor infertility. A total of nine oocytes were retrieved. Of these, seven were used with ICSI. Two were germinal vesicle (GV) oocytes. One of these two developed to metaphase II overnight. While using hyaluronidase (80 IU/ml) to remove the cumulus, the zona was damaged. Despite this, the oocyte was successfully injected with one spermatozoon. 3 days following ICSI, we changed the oocyte to
-minimal essential medium from human tubal fluid medium with patient human serum.
On day 3, the embryo underwent a compaction process and formed a compact morula (Figure 1
). By day 5, it had developed almost to something resembling a hatching blastocyst (Figure 2).
We believe that zona-free human oocytes can be successfully fertilized by ICSI and that fertilized zona-free human oocytes can undergo normal cleavage, compaction, blastocyst formation and a process similar to hatching in vitro. In conclusion, we feel that in cases where it is difficult to obtain quality oocytes, ICSI can be used even if the zona is not intact.
Notes
1 To whom correspondence should be addressed 
References
Ding, J., Rana, N. and Dmowski W.P. (1999) Intracytoplasmic sperm injection into zona-free human oocytes results in normal fertilization and blastocyst development. Hum. Reprod., 14, 476–478.
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