Background: The prevalence of asymptomatic bacteriuria (ASB) in pregnancy is 2-10% and is associated with both maternal and neonatal adverse outcomes as pyelonephritis and preterm delivery. Antibiotic treatment is reported to decrease these adverse outcomes although the existing evidence is of poor quality. Methods/Design: We plan a combined screen and treat study in women with a singleton pregnancy. We will screen women between 16 and 22 weeks of gestation for ASB using the urine dipslide technique. The dipslide is considered positive when colony concentration ≥105 colony forming units (CFU)/mL of a single microorganism or two different colonies but one ≥105 CFU/mL is found, or when Group B Streptococcus bacteriuria is found in any colony concentration. Women with a positive dipslide will be randomly allocated to receive nitrofurantoin or placebo 100 mg twice a day for 5 consecutive days (double blind). Primary outcomes of this trial are maternal pyelonephritis and/or preterm delivery before 34 weeks. Secondary outcomes are neonatal and maternal morbidity, neonatal weight, time to delivery, preterm delivery rate before 32 and 37 weeks, days of admission in neonatal intensive care unit, maternal admission days and costs. Discussion: This trial will provide evidence for the benefit and cost-effectiveness of dipslide screening for ASB among low risk women at 16–22 weeks of pregnancy and subsequent nitrofurantoin treatment. ; Brenda M Kazemier, Caroline Schneeberger, Esteriek De Miranda, Aleid Van Wassenaer, Patrick M Bossuyt, Tatjana E Vogelvang, Frans JL Reijnders, Friso MC Delemarre, Corine JM Verhoeven, Martijn A Oudijk, Jeanine A Van Der Ven, Petra N Kuiper, Nicolette Feiertag, Alewijn Ott, Christianne JM De Groot, Ben Willem J Mol, and Suzanne E Geerlings