Acute pyelonephritis in pregnancy: an 18-year retrospective analysis.

OBJECTIVE: We sought to describe the incidence of acute pyelonephritis in pregnancy, and to assess its association with perinatal outcomes in an integrated health care system. STUDY DESIGN: A retrospective cohort study was performed using medical records on 546,092 singleton pregnancies delivered in all Kaiser Permanente Southern California hospitals from 1993 through 2010. These medical records include the perinatal service system along with inpatient and outpatient encounter files. Adjusted odd ratios (ORs) and 95% confidence intervals (CIs) were used to estimate associations. RESULTS: The incidence of acute antepartum pyelonephritis was 0.5% (2894/543,430). Women with pyelonephritis in pregnancy were more likely to be black or Hispanic, young, less educated, nulliparous, initiate prenatal care late, and smoke during pregnancy. Pregnancies of women with pyelonephritis compared to those without were more likely to be complicated by anemia (26.3% vs 11.4%; OR, 2.6; 95% CI, 2.4-2.9), septicemia (1.9% vs 0.03%; OR, 56.5; 95% CI, 41.3-77.4), acute pulmonary insufficiency (0.5% vs 0.04%; OR, 12.5; 95% CI, 7.2-21.6), acute renal dysfunction (0.4% vs 0.03%; OR, 16.5; 95% CI, 8.8-30.7), and spontaneous preterm birth (10.3% vs 7.9%; OR, 1.3; 95% CI, 1.2-1.5). Most of the preterm births occurred between 33-36 weeks (9.1%). CONCLUSION: We characterize the incidence of pyelonephritis in an integrated health care system where routine prenatal screening for asymptomatic bacteriuria is employed. Maternal complications are commonly encountered and the risk of preterm birth is higher than the baseline obstetric population.