Factors influencing abnormal cleavage of early embryos: time-lapse imaging analysis of 138,178 normally fertilized embryos

BACKGROUNDS: Abnormal cleavage (ABNCL) in early human embryos is a frequent phenomenon associated with impaired developmental competence and reduced reproductive potential. However, the clinical determinants of ABNCL and its subtypes remain insufficiently defined. This study aimed to identify patient- and treatment-related factors associated with ABNCL in embryos generated through in vitro fertilization. METHODS: This retrospective cohort included 138,178 normally fertilized embryos cultured in a time-lapse imaging (TLI) system, comprising 77,260 normal cleavage (NC) and 60,918 ABNCL embryos. Univariate, stratified, and multivariable logistic regression with generalized estimating equation (GEE) analyses were performed to evaluate the associations between clinical characteristics-including demographics, controlled ovarian stimulation (COS) parameters, and insemination methods-and ABNCL occurrence and its subtypes. ABNCL was classified into direct cleavage (DC; including DC1 and DC2), rapid cleavage (RC), chaotic cleavage (CC), and other atypical patterns according to established morphokinetic criteria. RESULTS: Among the 138,178 embryos analyzed, 55.9% exhibited NC and 44.1% demonstrated ABNCL. Stratified analyses revealed significant variability in ABNCL rates across baseline characteristics and stimulation-related factors. In GEE models, endometriosis, unexplained infertility, higher oocyte yield, intracytoplasmic sperm injection (ICSI), and rescue ICSI were independently associated with an increased risk of ABNCL. Conversely, the use of a mild stimulation protocol and higher estradiol (E2) levels on the hCG trigger day were linked to a reduced risk. Subtype analyses showed distinct factor-specific patterns: higher total gonadotropin (Gn) doses increased the likelihood of DC and "other" ABNCL types, while elevated initial Gn doses were associated with higher risks of RC and CC. Additionally, the gonadotropin-releasing hormone antagonist protocol specifically increased the risks of RC and "other" ABNCL patterns. CONCLUSIONS: ABNCL is a common event during early embryo development and is significantly influenced by both patient characteristics and treatment strategies. Endometriosis, unexplained infertility, higher oocyte yield, ICSI, and rescue ICSI were associated with increased ABNCL risk, whereas mild stimulation and higher E2 levels on the trigger day appeared protective. These findings underscore the importance of individualized COS and fertilization strategies to promote optimal early embryo development in assisted reproductive technology; however, their implications are limited to cleavage-stage outcomes and should not be extrapolated to later developmental or clinical endpoints.