Hear It From a HealthLynked Provider: About Fetal Circulation

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If you’ve ever been curious about the development of a fetus or how babies breathe in the womb, tuck in for another edition of Oohvie’s “Hear It From HealthLynked” blog series where real providers share their research, thoughts, and publications on modern medical trends, technologies, and treatments. In this segment originally published in the Journal of Diagnostic Medical Sonography, HealthLynked ultrasonographers discuss how naturally occurring vascular shunts allow fetuses to reach maturity.

 

Agenesis of the Ductus Venosus with Extrahepatic Umbilical Vein Connection into the Right Atrium

by Sharon Gore RDMS RDCS, Melissa Smith RDMS, RVT RDCS, Colleen Nessling, BSRT RDMS

The fetal circulation differs from that of the adult. In the fetus the placenta serves as the fetal lungs because the fetal lungs do not function. In the fetus the left umbilical vein carries richly oxygenated blood from the placenta to the fetal heart. The right and left umbilical arteries take the deoxygenated blood back to the placenta to be reoxygenated.

Because the lungs are not needed in utero, some of the blood from the left umbilical vein goes to the liver sinusoids which are the basic units of the liver. Enough blood will go to these cells to keep them functioning, however most of the blood bypasses the sinusoids by a temporary vascular shunt called the DUCTUS VENOSUS.  The ductus venosus then empties the blood into the inferior vena cava and lastly into the right atrium of the fetal heart.  This temporary trumpet shaped vascular shunt has a sphincter mechanism within it.  This sphincter allows the ductus venosus to close and therefore prevent overload of the heart during contractions of the uterus.  This fact makes the ductus venosus very important for the fetus as a measure of protection from venous overload. After birth, the ductus venosus closes from a decrease in pressure by 1 to 3 months of age.  After closing the ductus venosus becomes a ligament within the infant liver.

Absence of the ductus venosus is a rare occurrence.  Aberrant connection of the umbilical venous circulation may take four forms:

  1. The umbilical vein bypasses the liver and connects directly into the inferior vena cava.
  2. The umbilical vein bypasses the liver and drains into the renal or iliac veins.
  3. The umbilical vein bypasses the liver and drains into the portal vein.
  4. The umbilical vein bypasses the liver and drains directly into the right atrium of the fetal heart.

The last type of connection that is associated with absent ductus venosus is the most common and generally carries the worst prognosis which may lead to congestive heart failure.  Agenesis of the ductus venosus is a rare anomaly in which sonography and color doppler showing blood flow in the fetus is used to watch for signs of heart failure and help lead to a positive outcome in the fetus. Sonography can incorporate a scoring system called the CVP (cardiovascular profile) into the ultrasound scan when absent ductus venosus is present.

The CVP has proven to be a valuable tool to assess fetal cardiac well-being.  Starting with 10 points, scoring the CVP involves subtracting up to 2 points in each of five categories and thus evaluating for heart failure.  These categories include evaluating for an enlarging heart, presence or absence of regurgitation in the heart valves, presence of hydrops or effusion and presence of absence of end diastolic flow in the umbilical artery. Overall, the lower CVP score the worse the prognosis and greater risk for cardiac failure.

In this case report a 25-year-old woman was scanned at 18 weeks and five days.   Sonography revealed no visualization of the ductus venosus and the umbilical vein was noted to enter the fetal abdomen and connect directly into the right atrium of the fetal heart. The patient was referred to a pediatric cardiology center for a fetal echocardiogram and they confirmed the diagnosis. At that time no evidence of congestive heart failure was noted.

Follow up sonography showed the right atrium to be enlarged along with prominent hepatic arteries.  Subsequent ultrasounds revealed pulmonary regurgitation and mitral and tricuspid valve regurgitation. At 25 weeks a small pericardial effusion was present.  At that point the patient was started on digoxin 0.25 mg twice daily.  By 29 weeks there was improvement in the CVP score but there was still elevated peak systolic velocity in the ductus arteriosus.

The patient presented to the hospital at 37 weeks and after birth the neonate was then transferred to a children’s hospital for evaluation secondary to the prenatal diagnosis of agenesis of the ductus venosus.  The neonate had an uneventful hospital stay and was released 9 days later and the infant went on to develop normally without complications.

[Read Full Publication]

 

Citation

Gore, Sharon, et al. “Agenesis of the Ductus Venosus With Extrahepatic Umbilical Vein Connection Into the Right Atrium.” Journal of Diagnostic Medical Sonography, vol. 29, no. 3, May 2013, pp. 133–136, doi:10.1177/8756479313480848.