Lower urinary tract infections (UTI) more readily evolve towards acute pyelonephritis (AP) during pregnancy. It should thus be considered as a serious situation. UTI screening is not routinely achieved but appears advisable because the treatment notably reduces the occurrence AP. The effectiveness of urinary testing by dipstick is good even though it can't compete with the sensitivity and specificity of urine culture. AP mainly increases the risk of prematurity. Prompt therapy should be carried out since renal function could be compromised by parenchymal infection. Unfavourable outcome mainly occurs in complicated UTI that it may reveal but that can often be drawn out form the patient's medical history.