Which of the following is a common soft marker for Down syndrome (DS) detected in the second trimester?

The presence of a thickened nuchal fold is a well-documented soft marker for Down syndrome when detected during the second trimester of pregnancy. This finding is typically assessed via an ultrasound and refers to an increased thickness of the skin fold at the back of the fetus's neck. A normal nuchal fold measurement is generally considered to be less than 6 mm; thickness greater than this may raise suspicion for chromosomal abnormalities, specifically trisomy 21 (Down syndrome).

Soft markers, such as a thickened nuchal fold, are not diagnostic by themselves but are used in conjunction with other tests and parameters to help assess the risk of Down syndrome. They have an important role in screening algorithms for trisomy 21, as they can indicate a need for further evaluation or testing.

While other conditions or factors may be observed during pregnancy, they do not serve as established soft markers for Down syndrome in the same way that a thickened nuchal fold does. For instance, short humerus may be suggested as another potential marker, but it is significantly less reliable than the nuchal fold measurement. Fetal macrosomia (increased fetal size) and increased fetal movement are generally not associated with Down syndrome risk and do not provide relevant