In normal pregnancy, there is a progressive increase in end-diastolic velocity due to growth and dilatation of the umbilical circulation. The resistance index therefore falls.
A resistance index >0.72 is outside the normal limits from 26/40 onwards.
In some pregnancies with IUGR and/or pre-eclampsia, there is a reduction in the diastolic velocity and in severe cases there is absent or reversed end diastolic velocity.
First published: 25/03/14