Past Issue

Volume 19, Number 3, Oct-Dec (Autumn) 2017, Serial Number: 75 Pages: 506-511

Determinants of The Grade A Embryos in Infertile Women; Zero-Inflated Regression Model

Amir Almasi-Hashiani, M.Sc, Azadeh Ghaheri, M.Sc, Reza Omani Samani, M.D., *,
Department of Epidemiology and Reproductive Health, Reproductive Epidemiology Research Center, Royan Institute for Reproductive Biomedicine, ACECR, Tehran, Iran
*Corresponding Address: P.O.Box: 16635-148 Department of Epidemiology and Reproductive Health Reproductive Epidemiology Research Center Royan Institute for Reproductive Biomedicine ACECR Tehran Iran



In assisted reproductive technology, it is important to choose high quality embryos for embryo transfer. The aim of the present study was to determine the grade A embryo count and factors related to it in infertile women.

Materials and Methods

This historical cohort study included 996 infertile women. The main outcome was the number of grade A embryos. Zero-Inflated Poisson (ZIP) regression and Zero-Inflated Negative Binomial (ZINB) regression were used to model the count data as it contained excessive zeros. Stata software, version 13 (Stata Corp, College Station, TX, USA) was used for all statistical analyses.


After adjusting for potential confounders, results from the ZINB model show that for each unit increase in the number 2 pronuclear (2PN) zygotes, we get an increase of 1.45 times as incidence rate ratio (95% confidence interval (CI): 1.23-1.69, P=0.001) in the expected grade A embryo count number, and for each increase in the cleavage day we get a decrease 0.35 times (95% CI: 0.20-0.61, P=0.001) in expected grade A embryo count.


There is a significant association between both the number of 2PN zygotes and cleavage day with the number of grade A embryos in both ZINB and ZIP regression models. The estimated coefficients are more plausible than values found in earlier studies using less relevant models.