Table 1 Definition of markers included in the study

1 Echogenic bowel (EB)

Areas of increased echogenicity in the fetal bowel that are as bright as bone. Single or multiple loops of bowel may be identified and it may be noted to be solid intraluminal echogenicity or occasionally echogenicity of the walls only (tram line).

Reported prevalence at fetal anomaly scan from previous studies [7, 9]: 0.2 – 1.4%

2 Mild to moderate ventriculomegaly (VM)

Mild to moderate ventriculomegaly is a ventricular atrial diameter, at any gestation, from 10 mm to 15 mm. Measurements are obtained from a transventricular axial view at the level of the glomus of the choroid plexus. The callipers were placed on the inner margins of the echogenic ventricular wall.

Reported prevalence at fetal anomaly scan from previous studies [19]: 0.1%

3 Pelvicalyceal dilatation (PCD)

Fluid filled dilatation of the renal pelvis measured on axial section with an anterior-posterior (AP) diameter of 5 mm or greater (callipers to be placed on the inner AP margins of the pelvic wall). This may be unilateral or bilateral.

Reported prevalence at fetal anomaly scan from previous studies [7, 8]: 0.3 – 4.5%

4 Nuchal thickening (NT)

Thickening of the skin and the subcutaneous tissues on the posterior aspect of the fetal neck. This is best viewed in a modified biparietal diameter (BPD) view to include the cavum septum pellucidum and cerebellum. Assessed by measuring the distance between the skin and occipital bone at the posterior aspect of the neck with the callipers placed on the outer edge of the bone and the outer edge of the skin. A measurement of 6 mm or greater was considered to indicate thickening before 20 + 6 weeks gestation.

Reported prevalence at fetal anomaly scan from previous studies [20, 21]: 0.4 – 0.6%

5 Choroid plexus cysts (CPC)

Small sonographically discrete fluid-filled spaces ≥ 5 mm within the choroid plexus and seen on scan as black echo-free areas. May be single, multiple, unilateral or bilateral.

Reported prevalence at fetal anomaly scan from previous studies [6]: 0.6 – 2.1%

6 Echogenic cardiac foci (ECF)

Echogenic area on the papillary muscle of either (usually left) or both of the atrioventricular valves.

Reported prevalence at fetal anomaly scan from previous studies [4, 5]: 0.5 – 4.9%

7 Short femur (SF)

Femur length which is below two standard deviations (3rd centile) for gestational age when measured with the shaft of the femur parallel to the transducer. Care must be taken to ensure that the entire diaphysis of the femur is measured. If the epiphyseal cartilages are visible they were not included in the measurement. It is assumed that the remainder of the skeleton is normal.

Reported prevalence at fetal anomaly scan from previous studies [7]: < 5%