The ductus venosus is a temporary blood vessel in a developing fetus. It plays an important role in distributing oxygen and nutrients throughout the fetal body, adapting the fetal circulatory system to operate differently from an infant or adult.
Understanding the Ductus Venosus
The ductus venosus is a shunting vessel located within the fetal liver. This narrow, trumpet-shaped vessel directly connects the umbilical vein, carrying oxygenated blood from the placenta, to the inferior vena cava (IVC) or the distal left hepatic vein. Its presence is exclusive to the fetal stage of development.
Formed from a network of veins during embryonic development, the ductus venosus’s structure allows it to act as a bypass, efficiently directing blood within the fetal circulatory system. This temporary vessel helps the fetus receive oxygen and nutrients before its organs are fully developed.
Its Role in Fetal Circulation
The ductus venosus shunts a portion of oxygenated, nutrient-rich blood from the umbilical vein directly to the inferior vena cava, bypassing the fetal liver. This bypass is important because the fetal liver is not yet fully mature and does not process blood like an adult liver. By diverting blood from the liver’s capillary network, the ductus venosus ensures highly oxygenated blood reaches the fetal heart and brain efficiently.
While animal studies suggested up to 50% shunting, human fetuses shunt less. For example, about 30% of umbilical blood flow shunts through the ductus venosus at 20 weeks, decreasing to 18% by 32 weeks. The remaining blood still flows through the liver, providing it with oxygen and nutrients. The ductus venosus works with other fetal shunts, like the foramen ovale and ductus arteriosus, to deliver oxygenated blood to the developing brain and heart.
After Birth: Transformation and Clinical Significance
Following birth, the ductus venosus undergoes a natural transformation as the newborn’s circulatory system adapts. Functional closure typically occurs within minutes to days, with structural closure, involving fibrous tissue, taking one to three months. This process is triggered by increased blood oxygen levels, which reduce prostaglandins, causing the vessel to constrict and close. Once closed, it becomes a fibrous remnant known as the ligamentum venosum.
Sometimes, the ductus venosus fails to close properly after birth, a condition known as a patent ductus venosus (PDV). If it remains open, blood can continue to shunt, potentially leading to an intrahepatic portosystemic shunt, bypassing the liver’s filtration system. This can result in health concerns, including issues with oxygenation, heart strain, and liver dysfunction like encephalopathy. Premature infants may experience delayed closure compared to full-term babies.
In rarer instances, the ductus venosus might be absent, detectable during fetal development. An absent ductus venosus can be associated with other congenital anomalies, such as cardiac defects, chromosomal abnormalities, or issues with the gastrointestinal and genitourinary systems. Prognosis depends on whether the umbilical vein bypasses the liver entirely (extrahepatic drainage) or connects to the liver without the ductus (intrahepatic drainage); extrahepatic drainage generally has a less favorable outcome and higher risk of heart enlargement. Abnormal blood flow patterns, such as reversed flow, detected during pregnancy can signal potential issues like chromosomal abnormalities, heart defects, or growth restriction, and may be linked to adverse pregnancy outcomes.