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Uteroplacental circulation refers to the vascular connection between the maternal uterine circulation and the placenta, allowing oxygenated maternal blood to reach the intervillous space, where it interacts (without direct mixing) with fetal capillaries.

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Anatomy

A. Maternal Blood Supply to the Placenta

• Originates from the uterine arteries, which are branches of the internal iliac arteries.
• Uterine arteries → arcuate arteries → radial arteries → spiral arteries.

B. Spiral Arteries

• Invade the decidua basalis and open into the intervillous space.
• These vessels undergo physiological transformation in pregnancy:
  • Loss of muscular and elastic layers.
  • Result: Low-resistance, high-capacitance flow to support fetal needs.

2. Functional Circulatory Pathway

1. Oxygenated maternal blood is propelled through spiral arteries into the intervillous space.
2. It bathes the chorionic villi, which contain fetal capillaries.
3. Nutrient, gas, and waste exchange occurs across the syncytiotrophoblast layer.
4. Deoxygenated maternal blood drains via endometrial veins back to maternal circulation.

3. Physiological Features

• Volume of blood in the intervillous space: ~150 mL.
• Blood is replenished 3-4 times per minute to maintain adequate exchange.
• Total uterine blood flow increases significantly in pregnancy (~500–700 mL/min in the third trimester).