早产儿定义是

A.胎龄＞37周，体重＜2500g

B.胎龄＞37周，体重＜3900g

C.胎龄＞37周，体重＜2500g

D.胎龄＜37周，器官功能不成熟

E.不论胎龄大小，体重＜2500g