Pyelonephritis in Pregnancy

Pyelonephritis is an infection of the renal pelvis and kidney tissue, usually caused by bacteria ascending from the bladder. Pregnancy makes that ascent easier: progesterone relaxes ureteral smooth muscle, the ureters dilate, the enlarging uterus can impede drainage, and urinary stasis increases. Changes in bladder capacity can further promote incomplete emptying. Asymptomatic bacteriuria has no urinary symptoms, but it can seed an ascending infection. A single urine-culture screen during the first trimester is recommended for all pregnant women; treating a positive culture reduces the incidence of pyelonephritis. This is why a pregnant patient with fever and flank pain must not be approached as though she has uncomplicated cystitis: renal infection can deteriorate into maternal sepsis and can trigger uterine contractions or preterm labour.