de·cid·u·a 
(dĭ-sĭj-ə)
(dĭ-sĭj-ə)n. pl. de·cid·u·as or de·cid·u·ae (--ē′)
A mucous membrane lining the uterus, modified during pregnancy and shed at parturition or during menstruation.
[New Latin (membrāna) dēcidua, (membrane) that falls off, from Latin dēciduus, falling off; see DECIDUOUS.]
de·cidu·al adj.