Cervico-isthmic pregnancy carried to term.

A case of term pregnancy of cervical origin, defined as cervico-isthmic pregnancy, is described. Review of the literature suggested that similar cases originally described as term cervical pregnancies were actually cervico-isthmic. The occurrence of these rare cases is explained by successive thinning and unfolding of the isthmus from the direction of the cervix up to the closed, resisting anatomic internal os. The isthmus is thus incorporated into the cervical cavity; in a few exceptional cases this allows the development of the pregnancy to term. The most common clinical feature of these cases is the appearance of the vaginal portion of the cervix; it is shortened or effaced and softened, and the inferior segment bulges into the fornices.