Infections can have far-reaching consequences in pregnancy, both for mother and child. Some infections are more severe for women during pregnancy than outside of pregnancy. There are infections that can lead to birth defects, serious infections or even death in (unborn) children. Finally, the idea is that one of the pathways in which preterm birth can occur is due to infections. In this thesis, we focused on infections in pregnancy with special attention for urinary tract infections (UTIs). Since UTIs are the most common infection in pregnancy. An association between UTIs and (spontaneous) preterm birth was found in one of our studies. Risk indicators that are associated with UTIs in pregnancy were determined; the presence of asymptomatic bacteriuria and a history of recurrent UTIs. However, the diagnosis of a UTI in pregnant women is not easy. Symptoms of UTIs in pregnant women are most often not specific, and on the other side pregnancy can mimic UTI related symptoms, like frequent urination. It is likely that due to altered anatomy and altered hormonal status in pregnant women the results in a urine dipstick and urine sediment are different compared to the results in the general population. In a retrospective analysis we found that the laboratory findings of the urine dipstick had a low specificity. That is why we initiated the Urinary tract infections in Pregnancy (UP)-study. In this prospective cohort study we will revise symptoms of UTIs, the urine dipstick and the urine sediment in pregnant women.