chorion frondosum

The chorion frondosum is a crucial part of the developing placenta during pregnancy. It originates from the trophoblast, the outer layer of cells of the early embryo (blastocyst), which invades the uterine wall. As pregnancy progresses, the chorionic villi, which are finger-like projections from the chorion, grow larger on the side of the chorionic sac that faces the uterine wall. This specific region, where these villi develop extensively, is known as the chorion frondosum.1

The chorion frondosum, along with the decidua basalis (a maternal component of the uterine lining), forms the discus-shaped placenta. This organ facilitates the vital exchange of nutrients, oxygen, and waste products between the mother and the developing fetus through a specialized vascular system.12