Diagnostic accuracy of ultrasound screening for fetal structural abnormalities during the first and second trimester of pregnancy in low-risk and unselected populations

Objectives: This is a protocol for a Cochrane Review (diagnostic). The objectives are as follows:. The main objectives of this review are to assess the diagnostic accuracy of first- and second-trimester fetal anomaly screening in low-risk pregnant women, and to compare overall performance of single- and two-stage screening approaches with regards to the number of cases detected before birth, as well as the proportion of false positive diagnoses. Secondary objectives Our secondary objective is to identify potential sources of heterogeneity between studies by investigating the effect of clinical factors (i.e. prior testing, factors related to the conduct of the ultrasound examination, and healthcare setting of the study) and methodological factors (i.e. related to the study design, such as methods used for postnatal ascertainment of cases) on screening performance.