title: Birefringence parameter available for quantitative analysis of human zona hardness.
abstract: This study was designed to investigate whether a non-invasive birefringence parameter, determined using the Oosight™ imaging system, is useful for estimating the hardness of human zona pellucida (ZP). The value for retardance (R) × thickness (T), but not R or T alone, of ZP was positively correlated (r = 0.92, p < 0.0001) with its hardness estimated by the time required for a 0.1% protease solution to solubilize ZP at 37 °C. In a model experiment to induce ZP puncture by Fluorinert™ fluid microinjection (sham-hatching), the R × T value at the punctured site was positively correlated (r = 0.78, p < 0.01) with the hardness of the ZP as estimated by the maximum expansion rate. The R × T values of ZP in in vitro fertilization-derived embryos (21.6 ± 7.5) and intracytoplasmic sperm injection-derived embryos (20.8 ± 6.3) were significantly higher than that in unfertilized metaphase II oocytes (16.6 ± 6.1; p < 0.05). The R × T value after in vitro hatching of viable blastocysts (10.8 ± 6.2) was significantly lower than that of unexpanded morulae and early blastocysts (19.0 ± 4.0; p < 0.05), while the value of expanding blastocysts (15.3 ± 4.1) was intermediate. In conclusion, hardness of human ZP can be estimated non-invasively by birefringence-based microscopic observation.
authors.affiliation: Yamashita Ladies' Clinic, Kobe, Hyogo, Japan. hiwayama@hotmal.co.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Iwayama
authors.forename: Shinichi
authors.initials: S
authors.lastname: Hochi
authors.forename: Masanori
authors.initials: M
authors.lastname: Yamashita
mesh_terms: D001718:Birefringence; D005307:Fertilization in Vitro / Q000379:methods; D006801:Humans; D008677:Metaphase; D008859:Microscopy, Polarization; D009865:Oocytes / Q000648:ultrastructure; D015044:Zona Pellucida / Q000648:ultrastructure*