Abstract
Asymptomatic bacteriuria in pregnant women shall always be treated, because of the risk of development of acute pyelonephritis. Some antibiotics reduce the level of serum estriol and therefore are less suitable in the treatment of cystitis in the last trimester of pregnancy. Mecillinam is found effective against the most frequent urinary pathogen in cystitis in pregnancy (escherichia coli), and as it is found not to reduce the level of serum estriol it is concluded that pivmecillinam/mecillinam is an alternative in the treatment of symptomatic and asymptomatic urinary tract infections in the last trimester of pregnancy.