Chorionic

Chorionic is an anatomical term relating to the chorion, the outermost fetal membrane that surrounds the embryo in amniotes, including humans. In mammals, the chorion contributes to the fetal part of the placenta and participates in the exchange of gases, nutrients, and wastes between mother and fetus.

Structure and development

The chorion arises from the trophoblast and extraembryonic mesoderm. It forms two regions: the chorion frondosum, which contains chorionic villi that interface with the maternal endometrium, and the chorion laeve, the smooth portion facing the uterine wall. In humans, the chorion together with the decidua basalis forms the placenta; the fetal chorionic plate lies adjacent to the placental tissue, while the maternal side is organized as the decidual plate.

Clinical relevance

Chorionic villi extend into maternal tissue to establish nutrient and gas exchange. The term chorionic appears in several clinical contexts, such as chorionic villus sampling (CVS), a prenatal test that analyzes placental tissue for fetal genetic information early in pregnancy. Elevated or altered chorionic gonadotropin levels, produced by the placental trophoblast derived from chorionic tissue, are used in pregnancy assessment and monitoring.

Chorionicity and development

In multiple pregnancies, the number of chorionic sacs (chorionicity) defines the placental arrangement (e.g., dichorionic vs monochorionic). Chorionicity depends on the timing of zygotic splitting and has implications for fetal development and obstetric management.

Etymology

The term derives from Greek chorion, meaning a membranous outer layer.

Overall, chorionic describes aspects related to the chorion and its role in early development and placental function.