Extended embryo culture reduces the implantation rate on day 4 and day 5 when only a maximum of three embryos are cultured beyond the pronuclear stage

Objectives: To study the potential of embryo transfer after 3, 4 or 5 days of embryo culture under the Gem-tan embryo protection law according to which only a maximum of three zygotes are allowed to be cultured for embryo transfer. Study design: In a prospective study, 273 patients with assisted reproductive treatment were randomly allocated for transfer on days 3, 4 or 5. Pregnancy and implantation rates were evaluated in regard to day of transfer and results were compared by Chi-square or ANOVA test. Results: Out of 234 transfer cycles, 79 were performed on day 3, 76 on day 4 and 79 on day 5. Pregnancy and implantation rates were 41.8%/27.1% for transfer on day 3, 27.6%/14.1% for day 4 transfer and 16.5%/8.8% for transfer on day 5. These results were significantly different for pregnancy rates on day 3 versus day 5 (P < 0.001) and for implantation rates on day 3 versus day 4 (P < 0.005) and day 3 versus day 5 (P < 0.001). Conclusions: These findings suggest that extended embryo culture is not beneficial when the option for embryo selection at later stages of development is not available. (c) 2005 Elsevier Ireland Ltd. All rights reserved.