Unfortunately, as women mature and no longer present for family planning or antenatal care, smears are less likely to be done or the interval tends to exceed what is recommended. However, as the program develops and a computerized information system is developed, the recommended intervals will be increased. The effects of estrogen and vaginal pH gradually transform the endocervical epithelium into stratified squamous epithelium by a process of squamous metaplasia. This area is known as the transformation zone. It is the primary target of sampling for the Pap smear.
Squamous abnormalities arise in the transformation zone.
The position of the transformation zone varies according to age. In postmenopausal women the transformation zone is often located within the endocervical canal. An adequate Pap smear should provide representative assessment of the entire transformation zone. No single criterion determines adequacy. The presence of endocervical cells is suggestive that the area above the transformation zone has been sampled.