Tehran University of Medical Sciences Journal of Biostatistics and Epidemiology 2383-4196 8 3 2022 10 15 234 247 Kindu Gebre Department of Statistics, Haramaya University Shimels Gebre Departments of Software Engineering, University of Electronic Science and Technology of China, Chengdu, China Melkamu A. Zeru Department of Statistics ,BahirDar University 2021 07 10 2022 01 30 Introduction: Birth weight and gestational age are important determinants of an infant’s survival and future development. Low birth weight can be caused by preterm birth or by small gestational age. The main objective of this research was to identify the determinants of birth weight and gestational age simultaneously based on Ethiopia's demographic health survey in 2016 which implemented in a statistical package R. Methods: Cross-sectional study design was used from Ethiopia's demographic health survey in 2016. The bi-variate linear regression model was used to identify factors of birth weight and gestational age simultaneously which had small standard errors as compared to a separate model. Results: Bi-variate models of birth weight and gestational age determined the effect of predictors. Therefore, the model shows that the number of tetanus injections before pregnancy, educational level of a husband, desire for more children, drink alcohol, and region are statistically significant at 5% level of significance for gestational age in Ethiopia. Similarly, the size or height of a child at birth, preferred waiting time to another birth or birth interval, the number of tetanus injections before pregnancy was statistically associated with birth weight at 5% level of significance. Conclusion: From our finding, we concluded that the number of tetanus injections before pregnancy, educational level of a husband, desire for more children, alcohol drink, size or height of a child at birth, preferred waiting time or birth interval for another birth and region were significant predictors of birth weight and gestational age simultaneously at 5% level of significance. Hence, special care should be given to the pregnant during prenatal care for minimizing the risk of low birth weight and small gestational age https://jbe.tums.ac.ir/index.php/jbe/article/view/634