Ans. is 'a' i.e., DecreasesThe commonly used parameters in the umbilical aery doppler are:SD ratio: systolic velocity/diastolic velocityPulsatility index (PI) (Gosling index): (PSV - EDV)/ TAVResistive index (RI) (Pourcelot index): (PSV - EDV) / PSVNormally the parameters mentioned above should decrease progressively as the pregnancy advances, as there is increase in the end diastolic velocity due to growth and dilatation of umbilical circulation.Any detion in the parameters is suggestive of either IUGR or pre - eclampsia .Thus, during progressive monitoring of the umbilical aery Doppler, as the severity of the disease increases, we observe first:The decreased velocity in the end diastolic phaseThen absent flow in the end diastolic phase followed byReversal of flow in the end diastolic phase.