Introduction: Untreated urinary tract infection has some serious consequences for both the mother and the fetus. Since the majority of infections are in the form of asymptomatic bacteriuria, quantitative urine culture and screening should be done in all pregnant women at the initial prenatal visit. Materials & Methods: We conducted a cross sectional study in 1431 pregnant women referring to Ghods Hospital. Four hundred and ninety, 478 and 463 pregnant women were in the first, second and third trimester of pregnancy, respectively. For each pregnant woman urine culture and urine analysis was done. Antibiogram with disk diffusion test method was performed in positive culture. Results: In a total of 1431 women screened, 198 clinical specimens showed significant bacteriuria, representing a prevalence of 13.1%. The most common pathogens were E. Coli and Staphylococcus Saprophyticcus. Ampicillin was the most prevalent antibiotic in which resistance was reported. Cephalexin and Co-trimoxazole were the next and Nitrofurantoin was the least, respectively. Urine analysis was negative in 33% of culture positive specimens. There was a significant difference in asymptomatic bacteriuria between the first and third trimester with the second trimester of pregnancy. (P<0.027) Conclusion: Due to high prevalence of asymptomatic bacteriuria in pregnancy, urine culture is recommended in each pregnant woman in order to prevent severe maternal and neonatal consequences. Urine analysis is negative in nearly 1/3 of the positive results. Consequently urine culture is a gold standard procedure for detection of asymptomatic bacteriuria.