Soft markers for Down syndrome are features seen during a prenatal ultrasound at 16–20 weeks that may be signs that a fetus has Down syndrome.

Minor/Soft Markers; CNS: Ventriculomegaly Holoprosencephaly Microcephaly (biparietal diameter (BPD) < 1st percentile and HP/FL < 2.5th percentile) Dysgenesis of corpus callosum ...