Sunday, October 25, 2015
Antenatal ultrasound with Doppler assessment of fetal blood flow velocities has made it possible to detect a population of fetuses with poor growth and abnormal circulation. Absence or reversal of end diastolic flow (AREDF) in the umbilical artery is associated with poor outcome and thus elective premature delivery is common . Those preterm infants are at increased risk of adverse neonatal outcomes. Absence or reversal of end diastolic flow phenomenon occurs in approximately 6% of high risk pregnancies  and is believed to result from increased placental vascular resistance in response to both acute and chronic hypoxia. Lack of oxygen results in intrauterine growth restriction (IUGR) and the baby is often delivered preterm and small for gestational age. The prognosis is poor compared to those with normal antenatal Doppler studies . In infants with abnormal umbilical artery Doppler blood flow velocities it has been shown that blood flow to the head tends to be preserved to support growth of the brain at the expense of blood flow to the abdomen and growth of visceral organs . In the earlier stages of fetal hypoxia (before AREDFV occurs) the changes of cerebral redistribution may be seen, with widening of the ratio of blood flow velocity in the cerebral artery to that in the umbilical artery - the cerebro-placental ratio. An increase in this ratio has also been associated with increased perinatal morbidity .