Interest of co-cultures for embryos obtained by in-vitro fertilization: a French collaborative study.

Co-cultures of human embryos, particularly with Vero cells, are used by several French groups, mainly in cases of successive failures of implantation. In most cases co-culture is continued until the blastocyst stage, expanded if possible. A total of 1603 co-cultures have been performed by 11 groups over a 2-year period. Of these, 41.8% of cleaved eggs (day 2) reached the blastocyst stage at day 5 or day 6. The mean pregnancy rate and implantation rate per transfer were 32.9 and 24.8% respectively, which represented a significant improvement compared to the transfer of 2 day old embryos. The rate of multiple pregnancies remained high (29.1%), which implies that there should be transfer of not more than two blastocysts. The rate of anomalies perceived at birth or in utero was not different from the rate observed in the general population, taking account of the maternal age.