[New findings about placental circulation using ultrasound]

Introduction of transvaginal color Doppler has enabled precise analysis of placental circulation in early pregnancy. The purpose of this paper is to summarize the current understanding of the anatomy and physiology of the early placental circulation. Study of uteroplacental circulation has demonstrated a progressive decrease of peripheral resistance from large toward small branches during first and early second trimester of pregnancy. Doppler study of umbilical circulation has also shown a significant fall of resistance from umbilical artery to its branches. Analysis of uteroplacental circulation in abnormal early pregnancy has shown differences in comparison with normal values. Using of transvaginal color Doppler in early pregnancy is not successful in prediction of abnormal late pregnancy. Color Doppler is useful in diagnosis of placental and umbilical cord pathology. The duration of pulsed Doppler examination in early pregnancy should be reduced to minimum if we want to avoid excessive heating of embryonic tissue.