Table 1 Summary of EOD measurement by 3D TVS

Volume acquisition

 1. Reference plane: The mid-sagittal view of the cervix.

 2. Acquisition box and angle: adjusted to include the upper part of the cervix and the lower uterine segment containing the lower placental edge.

Volume display

 1. Plane A:

  a. The IO is centered in the plane.

  b. The reference point is positioned at the IO.

  c. Rotation around the z-axis to make the IO at the lowest level in the lower uterine segment.

 2. Plane B:

  a. The reference point is positioned in the middle of the upper edge of the cervical canal.

  b. Rotation around the z-axis to make the IO at the lowest level in the lower segment.

 3. Plane C:

  a. The reference point is positioned in the middle of the IO.

  b. Rotation around the z-axis to get the IO parallel to the y-axis.

 4. Plane A:

  a. Rotation 360° around the y-axis.

  b. Measure the shortest distance between the lower placental edge and the reference point (center of IO).