Normal placentation

The definitive placenta forms at 9-12 weeks of gestation and is made of:

• Basal or decidual plate attached to the uterine wall containing the tip of the spiral arteries and veins
• Chorionic or fetal plate to which the umbilical cord is attached and which contains the umbilicofetal circulation

The placental tissue is made of 15-30 cotyledons incompletely separated by septae created by the basal plate.

Each cotyledon consists of a main stem of a branching chorionic villus tree.

The septae help to direct maternal blood flow through the intervillous space.

The maternal blood flows through intervillous space and drains into uterine veins through the basal plate.