Influence of group culture and culture volume on the formation of human blastocysts: a prospective randomized study

The optimal culture conditions for embryos to reach the blastocyst stage are under investigation. One factor is the putative influence of autocrine or paracrine factors produced by the embryo itself. Studies in mice blastocysts showed a beneficial influence of micro-cultures and communal growth on pregnancy and implantation rates, attributed to these growth or survival factors. In humans, studies have only involved embryos up to day 2 or 3 without consistent results. Therefore a prospective, randomized study was designed to assess whether group culture or incubation volume would influence day 3 human embryos to develop into blastocysts. Embryos were initially cultured in groups until day 3, after which patients were randomly allocated to four groups. Group 1: group culture in a small volume; group 2: single culture in a small volume; group 3: single culture in a large volume; group 4: group culture in a large volume. No significant differences in blastocyst formation could be found between the four groups (35, 45, 36 and 36% respectively). Therefore any of the four modes can be used, whichever is most convenient. The only factor which made a statistically significant contribution was the number of embryos on day 3. An increase in the number of embryos by one embryo decreased the odds of obtaining a blastocyst by 6%. The overall pregnancy rate per transfer was 40%, and the implantation rate was 28%. Single culture in a small volume allows a direct and individual assessment of embryo morphology, and as such it seems preferable.