Why the foetal circulatory system is never directly connected to the mother blood vessels?

The fetal circulatory system is never directly connected to the mother's blood vessels to protect the fetus from potential immune reactions and blood type incompatibilities. Instead, the placenta serves as an intermediary, facilitating the exchange of oxygen, nutrients, and waste products while maintaining a barrier between maternal and fetal blood. This separation helps to ensure that the fetus develops in a controlled environment, minimizing the risk of infections and maintaining distinct blood circulations.