With regards to acute pyelonephritis in pregnancy all of the following are true except:
Pyelonephritis in Pregnancy:
Etiology:

Incidence in pregnancy is 1-3%
More common in primigravida and young females
Usually occurs in the second trimester after 16 weeks (>50%) but may occur in 1st and 3rd as well
Generally bilateral, if unilateral it is more common on right side (in more than half of the cases)
Most common organism responsible E. coli (70%), Klebsiella (10%).

Complications
Left kidney is involved in 50% of patients
Most common isolate is E. coli
More common in later 1/2 of pregnancy
Responds to amino glycosides