Objective: The objective of this article is to investigate whether in the clinical setting of second trimester ultrasound (US) investigations, 3D multiplanar correction prior to the measurement of Down syndrome (DS) facial markers (nasal bone length, prenasal thickness, fetal profile line, maxilla-nasion-mandible angle, prenasal thickness to nasal bone length ratio, and prefrontal space ratio) is superior to subjective judgment of a correct midsagittal plane by 2D technique. Methods: Measurements were performed on 2D images and 3D volumes (corrected to the midsagittal plane), acquired during the same scanning session. Results: All six markers were measured in 105 datasets (75 of euploid fetuses and 30 of DS fetuses). The maxilla-nasion-mandible angle measured on 2D images was significantly larger than on 3D volumes (p<0.01). In all other markers, there was no significant difference between measurements performed on 2D images or 3D volumes. No statistical difference was found for any marker between measurements performed on images acquired by either 2D or 3D US in their ability to discriminate between normal and DS fetuses. Conclusions: Nasal bone length, prenasal thickness, fetal profile line, prenasal thickness to nasal bone length ratio, and prefrontal space ratio can be confidently used as DS markers in second trimester US examinations performed by 2D US.