Which parameter on umbilical aery Doppler indicates imminent fetal demise

Earliest sign of fetal compromise is a raised S/D ratio in the Umblical aery flow. An absence of diastolic flow is indicative of severe fetal compromise and requires intensive fetal monitoring with NST and frequent doppler upto 34 weeks or occurence of reversal of flow (whichever is earlier) after which pregnancy should be terminated. A reversal of diastolic flow is indicative of imminent fetal death (fetus is expected to die within 24-48 hours) requiring urgent termination, and therefore reversal occuring before lung maturity carries poor chances of fetal survival