Fetal Circulation *Quick Explainer Video*

What is Fetal Circulation? We created this video to cover the medical definition and provide a brief overview of this topic.

➡️ Fetal Circulation
The process of fetal circulation is different from that of an adult because the fetus is not yet capable of breathing air and obtaining oxygen through the lungs. Instead, oxygen and nutrients are supplied to the fetus by the placenta via the umbilical cord. Oxygenated blood from the placenta enters the fetal body through the umbilical vein and flows into the hepatic circulatory system.

Approximately one-third of this blood goes to the lower trunk and extremities, while the other two-thirds flow through the ductus venosus and directly into the inferior vena cava. This blood in the inferior vena cava is well-oxygenated, but it mixes with venous blood returning from the lower extremities entering the right atrium. Around 50% of this mixed blood is shunted from the right atrium into the left atrium through the foramen ovale, which is a small opening in the interatrial septum. The left atrial blood then flows into the left ventricle and eventually into the ascending aorta, supplying the brain, brachiocephalic trunk, and descending aorta.

Venous blood from the superior vena cava is directed downward into the right atrium, then into the right ventricle, and finally into the main pulmonary artery. However, the relatively low PaO2 and the presence of prostaglandins in the fetal blood result in pulmonary vasoconstriction and increased pulmonary vascular resistance. This leads to a higher pulmonary artery pressure than aortic blood pressure. This causes approximately 90% of the blood entering the pulmonary artery to shunt through the ductus arteriosus, which is a muscular vessel connecting the trunk of the pulmonary artery to the aorta, into the systemic circulation.

Only the remaining 10% of blood actually flows into the lungs. The mixed blood flowing through the ductus arteriosus is routed into the systemic circulation, supplying some of it to the gut, lower extremities, and placenta. The exchange of gases and nutrients between the fetus and the mother takes place through the two umbilical arteries, which carry blood from the fetal abdominal aorta to the placenta. Fetal circulation is a crucial aspect of development and survival, providing the fetus with the oxygen and nutrients necessary for growth and development until it can breathe air and take in oxygen through the lungs.

➡️ Recap
During fetal circulation, 90% of blood bypasses the pulmonary circulation through the foramen ovale and ductus arteriosus (right-to-left shunting). Shunting that continues after birth is considered to be abnormal and may require medical intervention.

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🚑MEDICAL DISCLAIMER
This content is for educational and informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Please consult with a physician with any questions that you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you watch in this video. We strive for 100% accuracy, but errors may occur, and medications, protocols, and treatment methods may change over time.

💡AFFILIATE DISCLAIMER
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⏰TIMESTAMPS
0:00 - Intro
0:28 - Fetal Circulation
0:45 - Oxygenated Blood
1:38 - Venous Blood
2:27 - Mixed Blood
3:11 - Reminder

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