Background. To determine whether prolongation of embryo culture in vitro from day 2 to day 5 after ovum pick-up (OPU) and fertilization can improve the results of in vitro fertilization (IVF), and the morphology of the spare embryos on day 2 can predict the developmental capacity during prolonged culture. We also wanted to consider this as a strategy to avoid twin pregnancies if it could be possible to transfer only one blastocyst at a time in the future.
Methods. A retrospective analysis with embryo transfer timed according to the weekday of OPU. Embryo transfer was performed on day 2 in 103 cases and on day 5 in 120 cases. Only one cycle per couple was included.
Results. The pregnancy rates per embryo transfer on day 2 (27/103, 26%) and day 5 (36/120, 30%) were similar. There were significantly more miscarriages in the day 5 (50%) than in the day 2 group (22%, p = 0.02), but there was no significant difference in the baby take home rate (20% in day 2 group, 15% in day 5 group). The morphological appearance of the embryos on day 2 was poorly correlated to the developmental potential during prolonged culture in vitro. On day 5, transfer of one or two blastocysts resulted in a pregnancy rate that tended to be higher than that after transfer of morulae only.
Conclusion. Prolongation of embryo culture from day 2 to day 5 did not improve the clinical outcome of the IVF treatment when measured as baby take home rate. Therefore, for the time being, this strategy does not increase our chances to move towards single embryo transfer.