Screening for asymptomatic bacteriuria in pregnancy.

Objective: To compare the following 4 screening strategies for detecting asymptomatic bacteriuria (ABU) in pregnancy: urine testing with leukocyte-esterase-nitrite (LEN) strips at each prenatal visit followed by a urine culture if positive; a single urine culture at fewer than 20 weeks' gestation; 2 urine cultures, at fewer than 20 weeks' gestation and at 28 weeks' gestation; or 3 urine cultures, at fewer than 20 weeks', at 28 weeks', and at 36 weeks' gestation.

Methods: Participants were pregnant women presenting to 2 obstetricians and 6 family physicians at outpatient family medicine and obstetrical clinics in a large Canadian urban teaching hospital. LEN dipstick urine testing was conducted at each prenatal visit. A midstream urine culture was obtained from all women before 20 weeks' gestation and at 28 weeks' and 36 weeks' gestation, as well as for positive LEN tests. Any positive urine culture in an asymptomatic woman was designated a case of ABU. The total number of ABU cases that would be detected by each of the 4 strategies (LEN dipstick testing only, a single urine culture, 2 cultures, and 3 cultures) was determined and compared.

Results: There were 49 cases of ABU among 1050 women (4.7%). LEN testing at each prenatal visit identified 7 cases (14.3%), compared with 20 cases (40.8%) with 1 urine culture, 31 (63.3%) with 2 urine cultures, and 43 (87.8%) with 3 urine cultures.

Conclusion: A single urine culture before 20 weeks' gestation missed more than one-half the ABU cases. A culture in each trimester identified most ABU cases.