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A prospective, randomized study of 158 patients undergoing in-vitro fertilization (IVF) and embryo transfer was conducted to evaluate whether a shortened exposure of oocytes to spermatozoa enhances oocyte development, and subsequently influences the IVF outcome. A comparison was made between conventional treatment time and shorter exposure of retrieved oocytes to spermatozoa. Fertilization and cleavage rates, embryo quality, implantation and pregnancy rates in the study group (short exposure) versus controls (standard IVF procedure) were evaluated. Fertilization (56 versus 61%) and cleavage rates (96 versus 92%) were similar in the two groups respectively. However, embryo quality was significantly higher in the study group (P < 0.05). Moreover, the pregnancy and implantation rates were significantly increased (42.4 versus 26% per embryo transfer, and 16 versus 10% respectively; P < 0.05). Our results demonstrated that shorter exposure of oocytes to spermatozoa is superior to the standard time in IVF and may have a favourable effect on implantation rates by improving embryo quality.

Our study demonstrates that active and passive cigarette smoking increases the zona pellucida thickness of oocytes and embryos. Our findings also show that active and passive smoking has no significant effect on the thinning mechanism of the zona pellucida, which implies that it is independent of the initial zona pellucida thickness.

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