Prolonged blastomere movement induced by the delay of pronuclear fading and first cell division adversely affects pregnancy outcomes after fresh embryo transfer on Day 2: a time-lapse study

Abstract Research question What are the incidence, origin, and clinical significance of blastomere movement after the first cell division in the human embryo? Design A total of 1,096 embryos, which were cultured in the EmbryoScope+® time-lapse system and subjected to a single fresh-cleaved embryo transfer, were retrospectively analyzed. Type and duration of blastomere movement (dBMov) between the first (t2) and the second cell division (t3) was monitored, and the ratio of dBMov during the 2-cell stage [dBMov/(t3-t2)] was calculated. Morphological evaluation of embryos was performed by referring to the size of the blastomere and fragmentation after first division in addition to Veeck's criteria on day 2. The correlation between the dBMov and ongoing pregnancy was evaluated and the association of the dBMov with patient and embryonic characteristics was determined. Results Both movement type and the value of dBMov/(t3-t2) were significantly associated with asymmetrical first division, fragment formation, and morphological grade on day 2. Multivariate logistic regression analysis revealed that a higher value of dBMov/(t3-t2) significantly correlated with a decreased ongoing pregnancy rate, even after adjustment for co-founders (odds ratio: 0.399, P  = 0.0419). The time intervals of PN alignment and PN fading were significantly correlated with the dBMov/(t3-t2) value. Conclusions Embryos with extended blastomere movement after the first cell division, which is associated with the delay of PN fading and first cell division, have a lower competence to initiate an ongoing pregnancy after fresh embryo transfer on day 2. Thus, blastomere movement could be a useful predictive parameter for selecting embryos at the early cleavage stage.