Fractal analysis of zona pellucida thickness: bending energy as a predictive window on day 2 embryo fate

Abstract

OBJECTIVE: The quality of the embryo is crucial for the outcome of in vitro fertilization; however, the ability to accurately distinguish embryos with the highest reproductive potential from others is not entirely reliable. Most of the methods of classification of embryos in Assisted Reproductive Technologies (ART) are subjective and in clinical practice, there is still a lack of semi or fully automated procedures. Since measurement of Zona Pellucida Thickness Variability is a reliable parameter for assessing the embryo’s hatching capacity, we describe a new automatic method to record and quantify a new morphological parameter, the Local Zona Pellucida Thickness Variation (LZPTV) using an innovative fractal-based analysis similar to Bending Energy that captures the high-frequency variability of the thickness of the Zona Pellucida. PATIENTS AND METHODS: 436 digitized images of embryos obtained from 187 Intracytoplasmic Sperm Injection (ICSI) procedures, were evaluated retrospectively. The images of the embryos classified according to Veeck’s Embryo Grading Classification (VEGC) were processed by the software program “Embryon” for LZPTV computation. RESULTS: Patients with high LZPTV embryos had a significantly higher birth rate (54.7%) than patients with low LZPTV embryos (9.7%), or patients with Grade I VEGC (33.7%), the LZPTV measure also had a significantly higher specificity than the VEGC to predict pregnancy (83.5% vs. 53.8%) or delivery (80.2% vs. 49.1%). CONCLUSIONS: This new parameter, therefore, provides a reliable additional source of information that could be included in an integrative standardized approach in ART practice and research.

Keywords

• zona pellucida thickness
• bending energy
• fractal analysis
• embryo quality