This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General Embryology 1, Subject name: Anatomy
The intervillous space of the placenta contains 
Select and explain. 
A. Maternal blood, B. Fetal blood, C. Maternal and fetal blood, D. Amniotic fluid
A: Maternal blood
Answer: A: Maternal blood 
Explanation: The intervillous space contains only maternal blood as the spiral aeries of the endometrium penetrate the outer cytotrophoblast shell.