In umbilical artery Doppler, a S/D ratio greater than 3.0 is associated with what condition?

• A. S/D ratio less than 2.0
• B. S/D ratio greater than 3.0
• C. Absent end-diastolic flow
• D. Normal diastolic flow

Answer: (B)

An elevated S/D ratio in the umbilical artery Doppler reflects increased resistance in the placental circulation. When the S/D ratio is greater than 3.0, it signals abnormal placental blood flow and potential fetal compromise due to placental insufficiency. This threshold is used to flag the risk of decreased fetal perfusion, which correlates with conditions like fetal growth restriction. In contrast, a ratio below 2.0 suggests lower resistance and generally reassuring diastolic flow, and normal diastolic flow corresponds to a lower S/D ratio. Absent end-diastolic flow indicates even more severe impairment, often a later-stage or more critical finding, and is not the same as simply having an S/D ratio above 3.0, though related to high resistance.