Blastocyst collapse and cytoplasmic strings as complementary morphodynamic biomarkers of embryo competence and biochemical pregnancy.

Cytoplasmic strings (CS) and blastocyst collapse are dynamic features observed during embryo development in Assisted Reproductive Technology (ART) using time-lapse imaging. CS are filamentous projections connecting the inner cell mass and trophectoderm and may represent indicators of embryo competence, whereas blastocyst collapse has been associated with reduced viability. However, their clinical relevance remains unclear. This study evaluated the association between CS, blastocyst collapse, and ART outcomes in 276 blastocysts obtained from 177 couples undergoing homologous ART cycles between 2022 and 2024. Embryos were graded according to the Gardner classification and continuously monitored by time-lapse imaging to identify CS and collapse events. Associations with blastocyst quality and clinical outcomes, including β-hCG positivity, miscarriage, and live birth rate, were assessed. CS were detected in 61% of blastocysts and were significantly associated with higher morphological quality, being observed in 71% of top-quality, 57% of good-quality, and 32% of poor-quality blastocysts (p < 0.05). Blastocysts with CS also showed higher β-hCG positivity rates compared with those without CS (76% vs 51%; p < 0.05). Blastocyst collapse occurred in 34% of cases and was significantly associated with lower morphological quality, affecting 14% of top-quality, 29% of good-quality, and 43% of poor-quality blastocysts (p < 0.05). Collapsed blastocysts also showed lower β-hCG positivity rates (30% vs 39%; p < 0.05). An inverse correlation was observed between collapse timing and β-hCG levels. CS and blastocyst collapse may represent complementary non-invasive biomarkers of embryo competence and implantation potential.