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Objective: To compare cervical screening outcomes associated with age and three screening intervals, 1, 2, and 3 years.

Methods: We did a prospective cohort study comprising 128,805 women at community-based clinics throughout the United States who were screened for cervical cancer within 3 years of normal smears through the National Breast and Cervical Cancer Early Detection Program. We determined the incidence of cytologic abnormalities defined as atypical squamous cells of undetermined significance (ASCUS), low-grade squamous intraepithelial lesion (SIL), high-grade SIL, and suggestive of squamous cell cancer.

Results: Over the 3 years after normal smear results, the incidence of new smears interpreted as high-grade SIL or suggestive of squamous cell cancer (high-grade SIL or worse) was 66 of 10,000 for women under 30 years old, 22 of 10,000 for those 30-49 years, 15 of 10,000 for those 50-64 years, and 10 of 10,000 for those over 65 years. Age-adjusted incidence rates of high-grade SIL or worse were similar for women screened at 9-12 months (25 of 10,000), 13-24 months (29 of 10,000), and 25-36 months (33 of 10,000) after normal smears (P = .46). Age-adjusted incidence rates of ASCUS, the most common cytologic abnormality, did not change (P = .36). Incidence of smears interpreted as low-grade SIL increased as time from the normal smear increased (P = .01).

Conclusions: Within 3 years after normal cytology results, cervical smears interpreted as high-grade SIL or worse are uncommon, and the incidence rate is unrelated to the time since last normal smear. Optimal screening strategies for women with recent normal cytology results should be based on comprehensive modeling studies that incorporate the true risks and benefits of repetitive screening.

(C) 2000 The American College of Obstetricians and Gynecologists