Fetal arterial redistribution indicating true umbilical cord knot.

True umbilical cord knot often remains undiscovered prenatally due to a lack of characteristic clinical or ultrasound signs. We present a pregnancy with favorable outcome in which a non-stress test (NST) found non-reassuring fetal status. Abnormal Doppler blood flow patterns in the descending aorta and in the middle cerebral artery revealed fetal arterial redistribution with normal circulation in the umbilical artery despite a true cord knot. The benefit of fetal Doppler assessment is discussed. Increased aortic-cerebral ratio may reflect acute hypoxic compromise caused by the transitory constriction of the true umbilical cord knot with unrecognized morphologic and circulatory signs.