BackgroundAsymptomatic bacteriuria (ASB) is associated with adverse maternal and neonatal outcomes and is routinely screened for and treated in the first trimester. Prevalence of ASB in the second and third trimesters of pregnancy is unknown.AimsThe aim is to determine the prevalence of ASB in the second and third trimesters of pregnancy.MethodsProspective cohort study of 150 pregnant women. Mid‐stream urine samples were tested for ASB in the second (24–28+6) and third (32–36+6) trimesters. Women were assigned to one of two groups: (i) ASB in any trimester of pregnancy and (ii) no evidence of ASB in pregnancy. Maternal and neonatal outcomes were compared between groups.ResultsAmong 143 women included in the study, the rate of ASB was 4.9% (2.1, 2.1 and 3.2% in the first, second and third trimesters, respectively). Of those with ASB, 14% had it in every trimester, whereas 43% had it on two or more samples. Of those with ASB in pregnancy, 43% were detected for the first time in the third trimester. Rates of maternal and neonatal outcomes were not statistically significantly different between the two groups. No women with ASB were induced for chorioamnionitis or growth restriction.ConclusionThe rate of ASB was highest in the third trimester of pregnancy, with rates of 2.1, 2.1 and 3.2% in the first, second and third trimesters, respectively. This study was underpowered to assess maternal and fetal outcomes. Although numbers were small, the absence of ASB in the first trimester was a poor predictor of ASB in the third trimester.