Which of the following is true about the decidua?

• A. It is the name of the endometrium during pregnancy
• B. It forms the chorion
• C. It becomes the placenta
• D. It is the myometrium

Answer: (A)

Decidua is the endometrium after it has undergone decidualization during pregnancy. After implantation, the lining of the uterus transforms under hormonal influence and becomes the decidua, which lines the uterus and supports the embryo. It’s divided into portions (decidua basalis at the site of implantation, decidua capsularis over the implanted conceptus, and decidua parietalis lining the rest of the uterus). This tissue provides the maternal side of the placental interface and interacts with the fetal chorionic villi as the placenta forms. The chorion itself comes from the trophoblast and extraembryonic mesoderm, not from the decidua. The myometrium, the muscular layer of the uterus, is distinct from the decidua. So the statement that it is the name of the endometrium during pregnancy is the accurate one.