P-252 A roadmap to normal human embryo development – a timelapse study of embryos resulting in the live birth

Abstract

Abstract Study question What are the morphokinetic parameters of preimplantation development in normal human embryos? Summary answer We provide a timeline of early developmental events and the incidence of embryo morphological features compatible with childbirth. What is known already Timelapse embryo monitoring provides unique insight into early human development. Implementation of this technique in clinical practice allows for assessing developmental dynamics for improved embryo selection. Several markers and ranking algorithms have been proposed to predict blastulation or implantation outcomes, but only a few studies assessed time-lapse data with live birth as the primary endpoint. Therefore, the comprehensive morphokinetic profile of embryos that gave rise to live birth has not been defined. Study design, size, duration Retrospective observational analysis of 300 time-lapse records of IVF embryos known to develop into healthy newborns. Out of total 73 quantitative/qualitative signs annotated, we focused on 9 developmental events and 14 morphological features and evaluated their timing, duration, and incidence. The influence of potential confounding factors (i.e., egg age, donor egg, donor sperm, sperm quality, and sex of the child) was evaluated by advanced statistical methods. Participants/materials, setting, methods Embryo monitoring was performed by a GERI-timelapse incubator. Image acquisition of individual embryo development lasted 5-6 days, starting 10 minutes after ICSI, which was used as reference time point. Transmitted light images were automatically captured in 5-minute intervals and 7-11 focal planes. The embryo selection for transfer was based solely on its morphology. The annotation data represent the consensus of minimum 3 experienced embryologists. Generalized linear models were used to explore relationships between dataset variables. Main results and the role of chance The average age of female participants was 27.5 years; 71.67% of embryos were derived from young donor eggs without fertility disorders. The severe andrological factor was present in 8% of male patients; donor sperm was used in 23% of cases; 16% of embryos were derived from dysmorphic oocytes. Both sexes were equally represented among analyzed embryos. Our analysis showed that early development was characterized by remarkably short first mitosis (2.68 ± 0.73h) and the interval between the second and third division (t4-t3 = 0.65 ± 0.66h), whereas the third cleavage was less synchronous (t8-t5 = 5.46 ± 4.9h) No association between quantitative signs and confounding factors was found. Interestingly, 2-cell stage embryos often contained multiple nuclei in at least one blastomere (51%), but multinucleation was reduced at the 4-cell stage (8%). Multipolar divisions were absent during zygotic division and rare (2.3%) during the second cleavage. Preterm and partial compaction was observed in 26.6% and 34% of embryos, respectively. Importantly, we noticed that 11.6% of embryos in our dataset deviated from conventional scenario of cleavage dynamics. These “atypical” embryos were characterized by a significantly higher incidence of multipolar divisions during the second cleavage compared to “typical,” regularly dividing embryos. Additionally, the odds of partial compaction increase 10 times in “atypical” embryos. Limitations, reasons for caution The presented analysis only involved embryos confirmed to result in a live birth after transfer. The comparison with data from embryos that did not produce pregnancy was not performed because it would be impossible to discriminate between the role of the embryo and endometrial factors in implantation failure. Wider implications of the findings Human embryos may develop into healthy children despite irregular cell division. A high incidence of partial compaction in “atypical” embryos suggests a self-correction mechanism rescuing their developmental potential. A larger-scale analysis of features compatible with live birth is needed to improve embryo selection criteria for evidence-based decision-making. Trial registration number not applicable