A prospective study, using sibling oocytes, examining the effect of 30 seconds versus 90 minutes gamete co-incubation in IVF

BACKGROUND: Traditionally oocytes have been exposed to sperm overnight, for 16-20 h. This long period of co-incubation, however, has been shown to create problems with high levels of reactive oxygen species (ROS), which may affect embryo viability and cause hardening of the zona pellucida. Recently, a positive effect of reducing the co-incubation time to 90-120 min was reported. The objective of this study was to evaluate whether a further reduction of the co-incubation period could benefit the outcome of IVF. METHODS: In this prospective study, 777 sibling oocytes from 81 women undergoing IVF were divided via alternate allocation to co-incubation for either 30 s (ultrashort co-incubation) (group A) or for 90 min (standard co-incubation) (group B). Endpoints were normal fertilization (two-pronuclear, 2PN), polyspermy (>2PN), embryo quality (EQ), clinical pregnancy (CP) and implantation (IR). RESULTS: The normal fertilization rates of the two groups were comparable: group A 58.6% versus group B 58.0%. Significantly lower rates of polyspermy were seen in group A compared to group B (2.8 versus 7.2%, P = 0.008). No statistically significant differences in EQ, CP or IR were seen. CONCLUSION: This is the first study demonstrating the achievement of good fertilization rates in IVF with ultrashort co-incubation. Significantly lower rates of polyspermy were seen in the group with ultrashort compared to the standard co-incubation group. Further studies are, however, needed in order to evaluate whether ultrashort co-incubation has any effect on the outcome of IVF.