Received November 16, 2013
Accepted November 16, 2013

OBJECTIVE: to determine the blastocyst diameter, the Inner Cell Mass (ICM) diameter, and the proportion occupied by it, in relation with implantation and live birth rates. METHODS: A total of 118 IVF patients and 212 blastocysts with grade ≥3, by Gardner and Schoolcraft criterion were included. Embryos were cultured in sequential media (Vitrolife), until they reached blastocyst stage. Measurements of the blastocysts, ICM diameters and the proportion occupied by it were made, and related with implantation and birth live rates. Also, models were developed to predict the response variables. RESULTS: there wasn’t significant relation between blastocyst diameter and ICM diameter with the response variables. There was a significant association between the coefficient and implantation rates. In prediction models, the diameter of both structures was a good predictor of embryo implantation rate, for relatively large (> 162 μm) or small (< 130 μm) embryos. CONCLUSIONS: the ICM Diameter/ Blastocyst Diameter coefficient was the most important variable associated with implantation rate, while blastocysts and ICM diameters are good predictors of implantation rates, for relatively large or small embryos. The actual Gardner and Schoolcraft system for classification of human blastocysts is a good predictor of embryonic quality, and can be complemented with a criterion based on blastocyst diameter.