Figure 2. 40 MHz ultrasound biomicroscopy (UBM)-guided continuous wave (CW) Doppler measurements of umbilical blood flow. (a) In utero UBM image of an E12.5 mouse embryo (E), showing the Doppler sample volume (white box) positioned over the umbilical artery (A) and vein (V). The placenta is labelled as P. The scale bar is 1 mm. (b) CW Doppler waveform demonstrating arterial (A) flow towards the transducer (positive) and venous flow (V) away from the transducer (negative). Reprinted from [9] with permission.