Employed mothers face considerable amount of hazards. Especially shift work can impact pregnant women by affecting some hormones. This study was conducted to assess the adverse effects of shift work on pregnancy outcomes. This historical cohort study was conducted in 2017 in order to assess the effect of shift work on pregnancy outcomes. The subjects were consecutively selected from pregnant women, which referred to Al Zahra and Shahid Beheshti hospitals, Isfahan, Iran for their pregnancy care. The effect of shift work on pregnancy and labor complications (low birth weight, small for gestational age, pre-eclampsia and eclampsia, intra-uterine growth retardation, spontaneous abortion, preterm delivery, excessive bleeding during labor, and type of labor) was assessed. The effect was adjusted for occupation and number of children as well. Data were analyzed by SPSS (ver. 17) usingT-test, chi-Square test and logistic regression analysis. Totally, 429 pregnant women entered the study. There was not a statistically significant difference between morning and shift workers regarding age. It was found that shift work probably increases the incidence of small for gestational age, pre-eclampsia and eclampsia, intra-uterine growth retardation, spontaneous abortion, and preterm delivery, but after adjustment for job and number of children the effect was observed only on preterm delivery. Working in a rapid cycling schedule of shift work may cause an increase in the incidence of preterm delivery in pregnant mothers.