OP02.05: Disparities in first trimester screening in the US

Abstract

Objectives: Mid-sagittal plane for examination of the posterior brain is part of the routine 11–13 weeks scan, but the oblique axial plane is not. Our objective was to asses the feasibility of including visualization of the oblique axial plane in combination with midsagittal plane for examination of the posterior fossa as part of the routine 11–13 week scan. Methods: Transvaginal followed by a transabdominal 2D and 3D ultrasound scan were performed in 100 consecutive well dated 11–13 weeks normal fetuses. A protocol including habitual landmarks of the head for mid-sagittal and axial planes was considered. Also a more oblique axial plane to evaluated posterior fossa, the acute angle observed in the transition between cerebral peduncles and the thalami and specific distances was included. Results: In the mid-sagittal plane, the two echogenic horizontal lines, representing the posterior border of the brainstem and the choroid plexus of the fourth ventricle and the specific distances, were obtained in 72% of cases. In the axial plane, shape of the skull and butterfly like choroid plexus were seen in all cases. Oblique axial plane at the level of the diencephalon and midbrain was easily obtained, and the acute angle of the peduncles and thalamis were observed in 96%. Anteroposterior diameters of the cisterna magna and fourth ventricle, and the distance between the aqueduct of Sylvius and the occipital bone were seen in 94% of the cases. Intraand interobserver repeatability showed no differences. Conclusions: Oblique axial plane for examination of the posterior fossa is easy and fast, and should be considered in combination with the mid-sagittal plane part of a routine 11–13 week scan. However, more studies should be done to confirm its utility to detection of fetuses with spina bifida.