Doppler studis of foetus

·         Uterine artery Doppler:-In normal pregnancy the uterine artery PI decreases with fetal crown-rump length as CRL increases.  The uterine artery PSV should not be less than 60.  The Doppler indices generated automatically from the machine are  followings: the Pulsatility Index (PI), Resistance Index (RI) and S/D Ratio.cm/s

·         B) : What about Umbilical artery Dopler indices?? Ans:-- umbilical artery: the resistive index (RI) and pulsatility index (PI) slowly decreases for both through the course of gestation due to progressive maturation of the placenta and increase in the number of tertiary stem villi.

·          1)umbilical arterial S/D ratio (SDR): = systolic velocity / diastolic velocity

·          2) pulsatility index (PI) (Gosling index): (PSV - EDV) / TAV

·         3) resistive index (RI) (Pourcelot index): (PSV - EDV) / PSV

·         4) PSV: peak systolic velocity 

·         5) EDV: end-diastolic velocity 

·         6) TAV: time-averaged velocity-often not estimated.

The Doppler indices of umbilical artery have been found to decline gradually with gestational age (i.e. there is more diastolic flow as the fetus matures): For instance the S/D ratio mean value decreases with fetal age say at 20 weeks, the 50th percentile for the S/D ratio is 4, at 30 weeks, the 50th percentile is 2.83.at 40 weeks, the 50th percentile is 2.18.Whereas RI mean value decreases from 0.756 to 0.609, PI mean value decreases from 1.270 to 0.96.