The mouse is a common animal species used for translational studies. In reproductive studies, this animal is typically preferred over other models as the rodent placenta shows similarities to the human but has a relatively short gestational period. In mice, the transport of oxygen and nutrients between mother and fetus occurs in a restricted area of the placenta called the labyrinth zone. Here, we provide a detailed protocol to study labyrinth zone trophoblast proliferation and syncytial trophoblast identification using paraffin-embedded histological sections of the mouse placenta and immunohistochemistry. By describing step by step how to collect the mouse placenta and process and analyze the labyrinth zone, we hope to help other scientists understand the contribution of changes in placental transport function in their experimental model and therefore advance our understanding of mechanisms underlying pregnancy complications.