EMBRYO MORPHOLOGY OR CLEAVAGE STAGE - HOW TO SELECT THE BEST EMBRYOS FOR TRANSFER AFTER IN-VITRO FERTILIZATION

This retrospective study of 1001 in-vitro fertilization (IVF) cycles i ncluded a consecutive series of single transfers (n = 341), dual trans fers (n = 410) and triple transfers (n = 250) where all the transferre d embryos in each cycle were of identical quality score and identical cleavage stage, In our 2 day culture system, transfer of 4-cell embryo s resulted in a significantly higher implantation rate and pregnancy r ate (23 and 49%) compared with 2-cell embryos (12 and 22%) and 3-cell embryos (7 and 15%). Furthermore, the transfer of 4-cell embryos resul ted in a significantly higher pregnancy rate compared with embryos tha t had cleaved beyond the 4-cell stage (28%), The implantation rate (21 %) and pregnancy rate (43%) after transfer of embryos of score 1.0 wer e significantly higher than after transfer of embryos of score 2.0 (14 and 32% respectively), Transferring embryos of score 2.1 resulted in significantly higher implantation rates (26%) and similar pregnancy ra tes compared with score 1.0, Transferring embryos of score 2.2 - 3.0 r esulted in a significantly lower implantation rate (5%) and pregnancy rate (15%), A striking finding was that embryos of quality score 2.0 h ad a significantly lower implantation rate compared with embryos of qu ality score 1.0 and 2.1 and a significantly lower pregnancy rate compa red to embryos of quality score 1.0, We also found a lower implantatio n rate and pregnancy rate when transferring 3-cell embryos, These find ings may indicate periods of increased sensitivity to damage during th e cell cycle, In conclusion, these results substantiate the idea of th e superiority of 4-cell embryos and demonstrate that minor amounts of fragments in the embryo may not be of any importance, These findings m ay Call for a shift when weighing the two main morphological component s (quality score and cleavage stage) in the sense that reaching a 4-ce ll cleavage stage even with the presence of a minor amount of fragment s should be preferred to a 2-cell embryo with no fragments.