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Fetal circulation is unlike adult circulation as it uses physiological shunts to carry oxygenated blood to tissues and bypass developing organs. The viability of the fetus heavily relies on these shunts to adequately perfuse developing tissues and organs, especially the brain and heart. The ductus venosus is a shunt that allows oxygenated blood in the umbilical vein to bypass the liver and is essential for normal fetal circulation.[1] Blood becomes oxygenated in the placenta and travels to the right atrium via umbilical veins through the ductus venosus, then to the inferior vena cava.[1] This oxygenated blood then passes through the foramen ovale, an opening between the atria, into the left atrium to be distributed systemically.[1] Therefore, the ductus venosus plays a key role in maintaining this unique circulation pattern. Fetal circulation studies are done via Doppler ultrasound or MRI to ensure proper blood flow through these shunts.[2] If there is impedance or absence of flow through these shunts, it may correlate with aneuploidies, cardiac defects, and/or other postpartum disease states.[3] Postpartum, the ductus venosus closes, secondary to increased cardiac pressures and decreased circulating prostaglandins.[4] The ductus venosus is critical for proper fetal circulation, but disruption of flow in utero or failure to close this shunt postpartum can lead to many adverse antenatal and perinatal outcomes.

Abnormal fetal venous circulation is observable in patients with the absence of the ductus venosus with the main abnormalities being[10]: Umbilical vein bypasses the hepatic system and draining into the right atrium Umbilical vein connects directly to the inferior vena cava via iliac veins Umbilical vein drains into the portal circulation Researchers have noted that decreased or abnormal blood flow through the ductus venosus during the first trimester has links with aneuploidies such as trisomy 13, 18, 21, and Turner syndrome.[11] Therefore, Doppler during the first trimester is a beneficial screening tool for these conditions. Abnormal ductus venosus waveforms during atrial contraction are also associated with a three-fold increase in congenital heart defects.[12] Early fetal growth restriction can also be identified in the second trimester using ductus venosus Doppler, which shows increased shunting to preserve cerebral and cardiac blood flow.[8]