Tehran University of Medical Sciences Acta Biochimica Iranica 0001-5261 3 2 2025 05 20 109 113 Saeideh Abdolahpour Growth and Development Research Center, Children’s Medical Center, Tehran University of Medical Sciences, Tehran, Iran Maryam Nasri Growth and Development Research Center, Children’s Medical Center, Tehran University of Medical Sciences, Tehran, Iran Farzaneh Abbasi Growth and Development Research Center, Children’s Medical Center, Tehran University of Medical Sciences, Tehran, Iran Reihaneh Mohsenipour Growth and Development Research Center, Children’s Medical Center, Tehran University of Medical Sciences, Tehran, Iran Maryam Khazdouz Hazrat-e Ali Asghar Children’s Hospital, Iran University of Medical Sciences, Tehran, Iran Farshad Sharifi Elderly Health Research Center, Tehran University of Medical Sciences, Tehran, Iran Sedigheh Shams Children’s Medical Center, Tehran University of Medical Sciences, Tehran, Iran 2025 07 12 2025 07 20 Objectives: Transient Neonatal Tyrosinemia (TNT) is a benign, self-limiting disorder characterized by elevated blood tyrosine levels in neonates. It is often caused by immature hepatic enzymes, particularly 4-  ydroxyphenylpyruvate dioxygenase (4-HPPD), and may be influenced by factors such as prematurity, low birth weight, and high protein intake. Early detection via newborn screening is essential to differentiate TNT from more serious disorders such as tyrosinemia type I. The aim of this study is to determine the incidence of TNT and identify perinatal factors associated with its development in Iranian neonates. Methods: This retrospective case-control study reviewed newborn screenings performed at the Growth and Development Research Center’s metabolic laboratory between March 2019 and February 2023. The control group comprised newborns with normal metabolic screening results during the study period. Results: Metabolic screenings were conducted on 73,349 infants. The incidence of TNT was found to be 0.47%, corresponding to a total of 345 diagnosed cases. TNT infants had a lower gestational age (37.7 ± 1.4 weeks), lower birth weight ( 2.94±0.5kg), and a higher rate of cesarean deliveries (83.9%) compared to the control group (P < 0.05). Logistic regression analysis showed significant associations between TNT and preterm birth (OR: 868.2, 95% CI: 168.9–4212.7, P < 0.001), cesarean delivery (OR: 3.5, 95% CI: 2.26–5.3, P < 0.001), and gestational age (OR: 0.17, 95% CI: 0.12–0.24, P < 0.001). No significant association was found with other parameters (P ≥ 0.05). Conclusion: TNT incidence in Iranian newborns is associated with prematurity and cesarean delivery. Optimizing screening protocols and encouraging vaginal delivery when possible may reduce TNT rates. https://abi.tums.ac.ir/index.php/abi/article/view/139 https://abi.tums.ac.ir/index.php/abi/article/download/139/110