W2_Fetal Circulation & Doppler

What is one of the learning objectives of this lecture?

To describe how to perform, assess & report an umbilical artery Doppler examination correctly.

What is one of the key questions about umbilical artery Doppler examination?

What technique is required to perform a clinically useful Doppler examination of the umbilical artery?

What are some general rules to follow before starting a Doppler examination?

Know your US equipment, fluid dynamics, hemodynamics, and fetal physiology.

What are the fetal vessels discussed in the lecture?

Umbilical artery (UA), Middle cerebral artery (MCA), Ductus venosus (DV), Ductus Arteriosus, and Umbilical vein (UV).

What are the maternal vessels discussed in the lecture?

Uterine arteries (UtA).

What are the characteristics of fetal circulation?

High heart rate, low blood pressure, and low peripheral resistance.

What is the function of the ductus venosus shunt?

Connects the umbilical vein to the inferior vena cava, allowing highly oxygenated blood from the placenta to bypass the liver.

What is the function of the foramen ovale shunt?

Located within the atrial septum, enabling the shunting of oxygenated blood from the right atrium to the left atrium.

What is the function of the ductus arteriosus shunt?

Channels blood from the pulmonary artery to the aorta, diverting blood away from the lungs which are not yet functional.

What are the characteristics of placental circulation?

Has low impedance and high flow due to the large surface area of the placenta, facilitating efficient transfer of oxygen and nutrients from the mother's blood to the fetus.

What are the characteristics of pulmonary circulation?

Has high impedance and low flow in the fetus as the lungs are not yet fully developed, meaning most blood is shunted away from the lungs through the ductus arteriosus.

Why is delayed cord clamping practiced?

To allow for the maximum volume of blood to be transferred to the infant before disconnection from the placenta.

What are the benefits of delayed cord clamping?

Increases iron stores in the neonate, increases hemoglobin levels, and improves transitional circulation.

What percentage of adults have complete foramen ovale closure?

The foramen ovale only completely closes as expected in about 75% of adults.

What is a paradoxical embolus?

An embolus originating in systemic venous circulation that travels to the heart, crosses the heart laterally through the patent foramen ovale, and can result in a stroke.

What are some associations with a persistent ductus arteriosus?

Associations with congenital rubella infections and preterm delivery.

What type of medication may be used to treat a PDA?

Prostaglandin synthesis inhibitor.

What are the indications for Doppler in pregnancy?

Placentation, fetal well-being, hypoxaemia, and anaemia.

What do umbilical arteries do?

carry deoxygenated fetal blood to the placenta.

How to visualize the umbilical artery for Doppler assessment

Select a free loop, not too close to the fetal cord insertion or the placental insertion.

ISUOG recommendations for umbilical artery Doppler

Sampling in free-floating loops of umbilical cord in singleton. Fetus should be at rest and not breathing.

What happens to placental resistance as gestation advances?

Resistance in placenta decreases with advancing gestation.

What are some abnormal findings in umbilical artery Doppler?

Absent or reversed end diastolic flow.

Tips for umbilical artery Doppler.

Sample both umbilical arteries and use the more normal value. Sample approximately mid umbilical cord.

How to improve Doppler signals.

2D image in freeze mode provides better Doppler signals.

Abnormal UA findings

Elevated UA index, REDV.

Where should umbilical artery measurements be made?

Measurements should be made in a free cord loop.

When is umbilical artery assessment indicated?

Reduced fetal growth velocity/fetal growth restriction (FGR).

Why and when to use Uterine artery Doppler?

Screen for early onset preeclampsia. Assessment of suspected IUGR.

How to perform Uterine artery Doppler trans-abdominally?

The probe is placed longitudinally in the lower lateral quadrant of the abdomen, & angled medially.

What happens to Diastole in a normal pregnancy?

Diastole increases.

What is 'notching' in uterine artery Doppler?

Reduction in forward flow at the start of diastole.

Abnormal Uterine Artery Doppler measurements

Pl > 95th percentile. Bilateral notching after 24 weeks.

When are uterine artery measurements indicated?

Suspicion of placental insufficiency / FGR. FGR in previous pregnancy.