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Birefringence parameter available for quantitative analysis of human zona hardness

Published online by Cambridge University Press:  27 July 2010

Hiroshi Iwayama*
Yamashita Ladies’ Clinic, Kobe, Hyogo 651–0086, Japan.
Shinichi Hochi
Faculty of Textile Science and Technology, Shinshu University, Ueda, Nagano 386–8567, Japan.
Masanori Yamashita
Yamashita Ladies’ Clinic, Kobe, Hyogo 651–0086, Japan.
All correspondence to: Hiroshi Iwayama. Yamashita Ladies’ Clinic, Kobe, Hyogo 651–0086, Japan. Tel: +81 78 265 6475. Fax: +81 78 265 6476. e-mail:


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.

Research Article
Copyright © Cambridge University Press 2010

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