Background: Premature birth is the main cause of neonatal mortality and long-term complications, which imposes heavy financial and psychological burdens on the family and society; therefore, it is important to recognize the factors affecting it. Objective: The aim of this study was to determine the relationship between socioeconomic status, psychosocial factors, and food insecurity with preterm delivery. Materials and Methods: This longitudinal study was conducted on 674 pregnant women at 24-28 wk of gestation who met the inclusion criteria. The subjects were selected using cluster sampling. The pregnant women filled out total questionnaires of study and they followed up until delivery and the data about the newborn was collected after delivery. The data collection tools included questionnaires for evaluating socioeconomic status, psychosocial factors, and food insecurity. Results: The prevalence of preterm delivery was 7.7%, and socioeconomic factors were not associated with preterm labor. Among the intermediary factors, social health, food insecurity, stress, and prenatal care had a significant relationship with preterm labor. The prevalence rates of preterm delivery in cases with food insecurity, stress, and inadequate prenatal care were 2, 9.1 and 13.2 times higher than those who had food security, did not experience stress, and received adequate care during pregnancy. Conclusion: Preterm labor is a relatively common problem in which intermediary social determinants of health can play an important role. Considering the limited studies on this issue, the results of this study can lay the foundation for future studies.