The principle of B-ultrasound technology to predict fetal gender The principle of B-ultrasound technology to predict fetal gender is to determine the gender of the fetus by detecting the reflection and absorption of sound waves by the fetus in the mother\’s womb and observing the reproductive organs near the fetus\’ arrangement in the color ultrasound image. When B-ultrasound detects the gender of the fetus, it uses high-frequency sound waves, which are non-invasive and non-radiative, and are harmful to both the mother and the baby.