What does decidua mean?
The decidua is the specialized layer of tissue that lines the inside of the uterus during pregnancy. Derived from the ordinary endometrium, it undergoes profound change under the influence of pregnancy hormones, thickening into a soft, nutrient-rich bed in which the fertilized egg implants and through which the growing fetus draws sustenance from its mother's body. Because it forms the maternal contribution to the placenta, the health of the decidua is central to normal fetal development, and clinicians distinguish named regions of it — the decidua basalis, capsularis, and parietalis — according to their position relative to the embryo. After childbirth, most of the decidua detaches and leaves the body together with the placenta, a fact reflected in its very name: it comes from the Latin decidere, meaning 'to fall off'. The word belongs firmly to medical and scientific register and is seldom heard outside those fields, yet it captures one of the more remarkable feats of human physiology — a living lining built anew, and then deliberately discarded, with every pregnancy.
nounThe modified mucous membrane lining the uterus during pregnancy, which thickens to receive and nourish the embryo and is largely shed at childbirth.
- The modified endometrium (uterine mucosa) of pregnancy, which thickens under hormonal influence to support the implanted embryo and forms the maternal part of the placenta.
- By extension, the portion of this membrane shed at parturition or menstruation.
"During implantation, the embryo embeds itself deep within the decidua of the uterine wall."
"Pathologists examined the decidua for signs of abnormal implantation."
"At delivery, much of the decidua separates and is expelled along with the placenta."
Both plurals are attested; the Latinate 'deciduae' appears in older or more formal texts, while 'deciduas' predominates in modern usage. In practice the word usually occurs in the singular.
"Histological sections of both deciduae were compared under the microscope."
Named from Latin for 'that which falls away', the decidua is literally the tissue your body builds and then discards with each pregnancy — biology's own built-in disposable lining.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of decidua
Decidua was adopted into English in the late 17th century directly from New Latin, where it served as a shortened form of the phrase membrana decidua, 'the shedding membrane'. The underlying Latin verb decidere combines the prefix de- ('down, away') with cadere ('to fall'), the same root that gives us decide, accident, and incident, as well as the adjective deciduous. Anatomists chose the name because the membrane visibly falls away at birth, making it a rare instance of a body part named for its own departure.
Related word forms
How decidua is actually used
Strictly technical vocabulary confined to medicine, embryology, and anatomy; rarely encountered outside clinical or academic contexts. It is almost always used in its singular form and typically appears with a qualifying anatomical term such as basalis, capsularis, or parietalis when precision matters.
Easily confused with decidua
Deciduous is an adjective describing trees that shed their leaves annually, while decidua is a noun referring specifically to the pregnant uterine lining that sheds at childbirth.