ULTRASOUND BIOMETRY OF THE FETUS. ´ULTRASOUND BIOMETRY OF THE FETUS Beyond the 8th week of pregnancy the embro becomes a fetus. The fetus can be visualized by analyzing the reflection of ultrasounds produced by ultrasonography, particularly well adapted for exploring fluid-containing organs such as the uterus during pregnancy.The human fetus develops in the womb surrounded by a membranous pouch containing amniotic fluid, that develops within one week of conception. Shown here, close-up of the