📘 Essential for Obstetrics, Pediatric Nursing, and Anatomy Exams
Fetal circulation is the blood flow system of the fetus that allows oxygen and nutrients from the placenta to reach fetal tissues, bypassing the non-functioning fetal lungs.
✅ “Fetal circulation refers to the unique system of blood flow that supplies oxygenated blood to the fetus through the placenta and bypasses the fetal lungs and liver via special shunts.”
🔹 Fetal lungs are non-functional → gas exchange occurs in the placenta
🔹 Oxygenated blood comes from the mother via the umbilical vein
🔹 Specialized shunts help direct blood to vital organs and bypass lungs/liver
| 🩸 Vessel | 📌 Function |
|---|---|
| Umbilical vein (1) | Carries oxygenated blood from placenta to fetus |
| Umbilical arteries (2) | Return deoxygenated blood from fetus to placenta |
| 🔀 Shunt | 📍 Location | 💡 Function |
|---|---|---|
| Ductus Venosus | Liver (umbilical vein → IVC) | Bypasses liver → sends blood to inferior vena cava |
| Foramen Ovale | Between right and left atrium | Bypasses lungs → blood goes directly to left atrium |
| Ductus Arteriosus | Pulmonary artery → Aorta | Bypasses lungs → connects pulmonary artery to aorta |
1️⃣ Oxygenated blood from placenta → umbilical vein
2️⃣ Most blood bypasses liver via ductus venosus → enters inferior vena cava (IVC)
3️⃣ Blood enters right atrium
4️⃣ Majority passes through foramen ovale → left atrium → left ventricle → aorta → brain and upper body
5️⃣ Deoxygenated blood from upper body returns via superior vena cava (SVC) → right atrium → right ventricle
6️⃣ From right ventricle → pulmonary artery, but most bypasses lungs via ductus arteriosus → descending aorta
7️⃣ Deoxygenated blood returns to placenta via umbilical arteries
| 🟢 Structure | 🔄 Becomes After Birth |
|---|---|
| Ductus Venosus | Ligamentum venosum |
| Foramen Ovale | Fossa ovalis (closes due to lung expansion) |
| Ductus Arteriosus | Ligamentum arteriosum |
| Umbilical vein | Ligamentum teres of liver |
| Umbilical arteries | Medial umbilical ligaments |
✅ These changes are triggered by the baby’s first breath, which lowers pulmonary resistance and increases left atrial pressure.
🔸 Patent Ductus Arteriosus (PDA) – failure of ductus arteriosus to close
🔸 Acyanotic congenital heart disease
🔸 Foramen ovale may remain open (PFO) – small shunt in some adults
🔸 Understanding fetal circulation helps manage fetal distress and congenital anomalies
🟡 Placenta acts as the lungs for the fetus
🟡 3 fetal shunts: Ductus venosus, foramen ovale, ductus arteriosus
🟡 Foramen ovale → allows blood from right atrium to left atrium
🟡 Umbilical vein carries oxygenated blood; arteries carry deoxygenated blood
🟡 Fetal circulation changes immediately after birth due to lung expansion
Q1. Which vessel carries oxygenated blood to the fetus?
🅰️ Umbilical artery
🅱️ Aorta
✅ 🅲️ Umbilical vein
🅳️ Pulmonary vein
Correct Answer: 🅲️ Umbilical vein
Q2. Which structure allows blood to bypass the fetal liver?
🅰️ Foramen ovale
🅱️ Ductus arteriosus
✅ 🅲️ Ductus venosus
🅳️ Umbilical artery
Correct Answer: 🅲️ Ductus venosus
Q3. The foramen ovale connects which two chambers?
🅰️ Right atrium – Right ventricle
🅱️ Left atrium – Left ventricle
✅ 🅲️ Right atrium – Left atrium
🅳️ Aorta – Pulmonary artery
Correct Answer: 🅲️ Right atrium – Left atrium
Q4. What causes the closure of ductus arteriosus after birth?
🅰️ Umbilical cord clamping
✅ 🅱️ Increased oxygenation from lung expansion
🅲️ Decreased fetal heartbeat
🅳️ Placental pressure
Correct Answer: 🅱️ Increased oxygenation from lung expansion
Q5. Which fetal vessel carries deoxygenated blood from fetus to placenta?
🅰️ Umbilical vein
✅ 🅱️ Umbilical arteries
🅲️ Aorta
🅳️ Hepatic vein
Correct Answer: 🅱️ Umbilical arteries