Age and time trends in the prevalence of cervical intraepithelial neoplasia on Papanicolaou smear tests, 1970-1988.

Substantial increases in the prevalence of cervical intraepithelial neoplasia (CIN) in women of all age groups are apparent from Papanicolaou smear test reports issued by the Victorian Cytology (Gynaecological) Service between 1970 and 1988. Most of the change in prevalence is due to an increase in reports of neoplasia of a lesser severity than CIN III. A progressive lowering of the age group having the highest prevalence of "definite" CIN is evident, from women aged 40-49 years in 1970-1973 to women aged 25-29 years in 1982-1988. The prevalence of "possible" CIN has consistently been highest among the youngest age groups screened. While 6.7% of screened women from the age group 20-24 years received a report of "definite" or "possible" CIN in 1988, only 0.08% of women in this group received a report of CIN III. Cohort analysis revealed that for women born between 1949 and 1958, the prevalence of CIN III continued to increase during 1988.