en other Orginal research <span style="font-size:14px;"><span style="font-family:Times New Roman;"><span style="line-height:2;"><span style="unicode-bidi:embed"><span style="color:#2980b9;"><b>Background<i>:</i></b> </span>Child growth is an important indicator of health from infancy to adulthood. Height and weight are widely used to assess the physical development and health of children. Since the effects of related factors may differ across the distribution of growth, joint quintile regression provides an appropriate method to identify heterogeneous associations.<span style="font-family:"Times New Roman",serif"></span></span><br> <span style="unicode-bidi:embed"><span style="color:#2980b9;"><b>Objectives:</b></span><b> </b>This study aimed to identify the factors influencing growth indicators of tow-year-old children using the joint quintile regression model.</span><br> <span style="color:#2980b9;"><b>Methods:</b></span><span style="color:black"> In this longitudinal study, data were obtained from health records of 420 children aged 24 months, covered by urban and rural health service centers in Zanjan province, Iran, in 2019, using two-stage cluster sampling. The joint quintile regression model was fitted by R 4.3.3.</span><br> <span style="unicode-bidi:embed"><span style="color:#2980b9;"><b>Results:</b> </span>The majority of children in the study were male (52.1%), urban residents (71.4%), and had mothers with diploma education (30.0%).<b> </b>The mean (SD) age of mothers was 30.70 (6.44) years. In all quintiles, gender, maternal age, gestational age (GA), maternal body mass index, and maternal education were positively and significantly associated with children&#39;s height and weight, except for maternal diploma education at the 0.25 quintile [95% CI (-0.05,0.03)]. Place of residence was negatively and significantly associated with both outcomes. Also, non-exclusive breastfeeding was negatively associated with children&#39;s height and weight at lower quintiles and positively associated at higher quantizes.</span><br> <span style="unicode-bidi:embed"><span style="color:#2980b9;"><b>Conclusion:</b></span> Considering the factors affecting child growth, paying attention to (gestational age, maternal education, place of residence, and exclusive breastfeeding) can be effective in promoting child growth.</span><br> &nbsp;</span></span></span> Weight, height, Child, Two-year-old, Joint Quantile Regression, Longitudinal Study 56 66 http://nmcjournal.zums.ac.ir/browse.php?a_code=A-10-1033-1&slc_lang=en&sid=1 Zahra Mohammadi zahramohammadi4020@gmail.com 100319475328460014507 100319475328460014507 No Department of Statistics and Epidemiology, School of Medicine, Zanjan University of Medical Sciences, Zanjan, Iran Ramazan Fallah rfvz@ums.ac.ir 100319475328460014508 100319475328460014508 No Department of Statistics and Epidemiology, School of Medicine, Zanjan University of Medical Sciences, Zanjan, Iran Parisa Khoshnevis Asl khoshnevis@zums.ac.ir 100319475328460014509 100319475328460014509 No Department of Pediatrics, Ayatollah Moussavi Hospital, School of Medicine, Zanjan University of Medical Sciences, Zanjan, Iran Farzane Ahmadi ahmadi.farzan@gmail.com 100319475328460014510 100319475328460014510 Yes Department of Statistics and Epidemiology, School of Medicine, Zanjan University of Medical Sciences, Zanjan, Iran