BACKGROUND Diagnostic ultrasound is used selectively in late pregnancy where there are specific clinical indications. However, the value of routine late pregnancy ultrasound screening in unselected populations is controversial. The rationale for such screening would be the detection of clinical conditions which place the fetus or mother at high risk, which would not necessarily have been detected by other means such as clinical examination, and for which subsequent management would improve perinatal outcome. OBJECTIVE To assess the effects on obstetric practice and pregnancy outcome of routine late pregnancy ultrasound, defined as greater than 24 weeks gestation, in women with either unselected or low risk pregnancies. METHODS The Cochrane Pregnancy and Childbirth Group Specialised Register of Controlled Trials and the Cochrane Controlled Trials Register were searched. METHODS All acceptably controlled trials of routine ultrasound in late pregnancy (defined as after 24 weeks). METHODS The principal reviewer assessed trial quality and extracted data, under supervision of the co-reviewer. RESULTS Seven trials recruiting 25,036 women were included. The quality of trials overall was satisfactory. There was no difference in antenatal, obstetric and neonatal intervention or morbidity in screened versus control groups. Routine late pregnancy ultrasound was not associated with improvements in overall perinatal mortality. Placental grading as an adjunct to third trimester examination scan was associated with a significant reduction in the stillbirth rate in the one trial that assessed it. There is a lack of data with regard to long term substantive outcomes such as neurodevelopment. There is a lack of data on maternal psychological effects. CONCLUSIONS Based on existing evidence, routine late pregnancy ultrasound in low risk or unselected populations does not confer benefit on mother or baby. There is a lack of data about the potential psychological effects of routine ultrasound in late pregnancy, and the effects on both short and long term neonatal and childhood outcome. Placental grading in the third trimester may be valuable, but whether reported results are reproducible remains to be seen, and future research of late pregnancy ultrasound should include evaluation of placental textural assessment.