Absent End Diastolic Umbilical Artery Doppler Flow Velocity (AEDV)

The umbilical cord is a soft, smooth, cord that connects the umbilicus of the fetus to the center of the placenta. The umbilical arteries carry deoxygenated blood from fetal circulation to the placenta. The two umbilical arteries converge together about at 5 mm from the insertion of the cord, forming a type of vascular connection called the Hyrtl's anastomosis (Basta & Lipsett, 2020). The primary function of Hartl's anastomosis is to equalize blood flow and pressure between the umbilical and placental arteries.

Circulation

Collectively the umbilical cord and the placenta aid in the flow and regulation of fetal circulation. The umbilical vein transports nutrients and oxygenated blood from mother to fetus. At midgestation about 30% of fetal cardiac output comes from umbilical blood. During the last trimester this percentage drops to about 20%.

The umbilical vein carries oxygenated blood to parts of the liver then flows to the inferior vena cava and foramen ovale of the fetal heart. Placenta and umbilical blood flow directly impact fetal Oxygen delivery (Basaa & Lipsett, 2020).

A decrease in blood flow leads to a decrease in oxygen to the fetus. Maintenance of patent umbilical arteries and baseline maternal arterial blood pressure is essential for maintaining sound cardiac output for the fetus.

Abnormal Umbilical Artery Flow

Abnormal umbilical artery flow with absent or reversed end-diastolic velocity (AREDV) during pregnancy is a strong indication of placental insufficiency. When AREDV occurs prenatally, a close follow-up or expeditious delivery should be contemplated.

REDV in the umbilical artery is associated with:

• intraventricular hemorrhage

• bronchopulmonary dysplasia and

• perinatal mortality.

It may also be associated with:

• respiratory distress syndrome

• necrotizing enterocolitis and

• long-term neurodevelopmental impairment (Wang et al., 2009).

Previous studies have clarified that an increased umbilical artery systolic/diastolic ratio is a significant risk factor for progression of:

• fetal acidosis

• fetal distress

• preterm delivery

• low Apgar scores and

• perinatal death.

Neonatal Complications Related to Abnormal Umbilical Artery Function & Formation

Intraventricular Hemorrhage (IVH)

In this condition, cerebral vasodilatation increases vascular wall strain and mechanical forces, which may contribute to IVH. On the other hand, AREDV in the umbilical artery also causes:

• fetal hypoxia

• acidemia

• platelet depletion and

• elevated nucleated red blood cells

This may cause hemorrhagic placental endovasculitis, infarction, and may subsequently increase the risk of brain injury (Wang et al., 2009).

Periventricular Leukomalacia (PVL)

PVL is the most important determinant of neurologic morbidity in children who are born prematurely and is considered a sonographic marker for cerebral palsy. In theory, blood–gas analyses from cordocentesis or immediately after birth have found a strong correlation between AREDV; moreover, studies of preterm fetal and newborn metabolic acidosis also suggested a higher risk of severe PVL.

Bronchopulmonary Dysplasia (BPD)

BPD is one of the most common respiratory complications in premature infants. The predisposing factors for BPD include:

• lung immaturity

• airway inflammation

• perinatal infection

• oxygen toxicity and

• barotrauma resulting from mechanical ventilation.

Furthermore, BPD is a significant risk factor for neurodevelopmental impairment and has been found to often correlate with AREDV.

Respiratory Distress Syndrome (RDS)

RDS is one of the leading causes of mortality and morbidity among premature neonates.

Necrotizing Enterocolitis (NEC)

The pathogenesis of NEC is not well understood and factors thought to increase the risk of intestinal injury include:

• prematurity

• intestinal ischemia

• enteral feeding and

• bacterial colonization

In fetuses with AREDV in the umbilical artery, especially combined with IUGR, circulatory redistribution increases blood flow to the brain (the brainsparing effect) and decreases blood flow to the viscera. Fetal hypoxia combines with increased mesenteric vascular resistance to predispose to intestinal ischemic injury; this may contribute to the development of NEC.

... and the list goes on:

• sepsis

• hypoglycemia

...

Truth is, there is still so much that we are learning about the brain; about the repercussions of injury to the brain.

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What Now?

If your client presents you with a brain-injured baby case, it is crucial for you to know if this case is meritorious or not. Opposing council will do everything in their power to argue:

1. The mother had pre-existing medical conditions that predisposed the infant to brain injury

2. Brain injury was caused by a malformation

3. A delay in response is not responsible for the brain injury

It is imperative to understand the medical innerworkings of such a case to:

1. ensure the case is indeed meritorious and not due to something such as Absent End Diastolic Velocity (AEDV)

2. determine the case to not be meritorious as not to spend time and money needlessly

There are some exceptions to these rules, as sometimes, supporting evidence can argue both.

For your birth injury cases, we at Saundra Smyrski LLC, are always ready! 727.225.4358