Figure 8a. Flash artifact due to motion of the fetal head. (a) US image of the cervix (C) and fetal head (H) obtained with fundal pressure being applied (left) shows a flash of color across the internal os simulating a vasa previa. On a US image obtained with no fundal pressure being applied (right), no color is demonstrated. (b) Doppler spectrum demonstrates the normal arterial flow pattern in a true vasa previa (compare with spectral noise in Figs 1d and 2c).