Do fetal and maternal blood mix during pregnancy?

During pregnancy, fetal and maternal blood typically do not mix due to the presence of the placenta, which acts as a barrier between the two circulatory systems. The placenta allows the exchange of oxygen, nutrients, and waste products without the direct mixing of blood. Maternal blood flows around the placenta in the intervillous space, and fetal blood circulates within the fetal blood vessels inside the chorionic villi; however, these remain separate. This separation is crucial for protecting the fetus from potential harmful substances and infections that could be present in maternal blood.

While there are rare circumstances, such as certain complications or trauma, where mixing could occur, under normal conditions, the blood of the mother and fetus remains distinct throughout the entire course of the pregnancy.