Reproductive Endocrine Assoc. Teaching and Clinical Research

Beneficial Effects Of Brief Coincubation Of Gametes I Human In Vitro Fertilization (IVF).
P. Quinn, M.L. Lydic, M. Ho, M. Bastuba, F. Hendee, A. Lachica, S.A. Brody. IVF Laboratory, Alvarado Hospital Medical Center, San Diego, CA and Division of endocrinology & Metabolism, UCSD School of Medicine, La Jolla, CA.

Objectives: The exposure of human oocytes to spermatozoa for 1 h gives equivalent fertilization rates and possibly better quality embryos than overnight coincubation; the presumptive fertilizing spermatozoon enters the cumulus mass within 15 min. and appears in the oocyte cortex within 4 h of insemination (Gianaroli et al., Human Reprod 11:166, 1996). This study was conducted to determine if a shortened coincubation time utilizing two different types of culture media, offered significant benefits to the outcome of IVF.

Materials and Methods: Fifteen sequential IVF patients had their gametes randomly divided into two groups and coincubated for either one hour or overnight (average lenth of coincubation 18 h; range 16 - 20 h). After the one hour coincubation, the oocytes were washed and transferred to fresh medium. The gametes were allocated between the two different culture media. The design was thus 2 x 2 factorial. The media used were Basal XI HTF which has no glucose (Glu) or phosphate (Pi) present and V12 HTF which is another modification of HTF which low Glu and no Pi (Quinn, Proc IX World Congress on Human Reproduction, Parthenon Publishing, 1996). Fertilization rates (FR) were recorded. Morphological quality of all resulting embryos was measured by an average cumulative embryo score (Steer et al., Human Reprod 7:117, 1992) on day 2 or 3 of culture at the time of replacement.

Results: There was no significant difference in FR between the 1 h or 18 h coincubation groups or between the two media treatment groups (overall FR - 1 h = 69%; 18 h = 74 %, P >0.8). However, the quality of the embryos was significantly better in the 1 h exposure group compared to the 18 h group (P<0.05, Sign test). The embryos in Basal XI HTF tended to be of better quality than there siblings in V12 HTF but there were insufficient data points to generate a significant effect. The 15 patients in this study had all embryos from all treatment groups replaced, resulting in 12 pregnancies (80%), 11 of which are ongoing, with an implantation rate of 0.39.

Conclusion: These results confirm previous observations that a brief 1 h exposure of human oocytes to the relatively large number of spermatozoa normally used in a standard IVF procedure can produce the same FR as overnight gamete coincubation. In addition, the brief exposure results in embryos of superior morphological quality. The prolonged exposure of oocytes to overnight coincubation with spermatozoa most likely creates suboptimal culture conditions due to the excessive generation of reactive oxygen species. This could be a likely explanation for the observed decrease in morphology score for the embryos obtained after overnight coincubation of gametes. These studies support the conclusion that coincubation of oocytes and spermatozoa for a shorter period of time is superior to the generally accepted overnight protocol.

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