Doppler analysis of the umbilical artery: why we must prefer the free loop of the cord.

Aim: The main objective was to confirm with modern tools the former assertion that there is a vascular resistance gradient along the umbilical cord.

Methods: We performed a prospective observational study in a population of women with third trimester monofetal and uncomplicated pregnancies during two months. Pulsatility Index and Resistance Index were calculated on three sites: placental end, free loop and fetal end of the cord.