Obstetric ultrasonography: recent observations in first trimester of pregnancy.

It is possible both to accurately measure foetal size and visualize the yolk sac and the amniotic membrane by ultrasound scanning in the first trimester of pregnancy. In threatened abortion an intrauterine haematoma or a foetal size smaller than normal are ominous signs. Likewise, too small a foetal size in early diabetic pregnancy indicates an increased risk of foetal malformation.