Five-Year Risk of CIN3+ After CIN1 Biopsy in a Norwegian Screening Setting: Comparison of CIN1 Diagnosed in a Single Calendar Year and in Two Consecutive Calendar Years.

Cervical intraepithelial neoplasia grade 1 (CIN1) is usually managed conservatively, but uncertainty remains about the subsequent risk of clinically significant high-grade disease, particularly after repeated CIN1. We conducted a retrospective population-based cohort study using anonymized cervical cytology, HPV, and histopathology records from Northern Norway from 2011 to 2025. We described temporal trends in screening-related outcomes and estimated the 5-year risk of CIN3+ after histologically confirmed CIN1 diagnosed in a single calendar year or in two consecutive calendar years. Across 2011-2025, the annual datasets comprised 334,471 screening records; 35,796 had ASC-US+ cytology (10.7%), 29,723 had a positive HPV test (8.9%), 35,416 underwent biopsy (10.6%), and 7870 were diagnosed with CIN2+ (2.4%). HPV positivity increased from 0.9% in 2011 to 15.7% in 2025, whereas CIN2+ detection peaked at 3.1% in 2018 and declined to 1.8% in 2025. In person-based analyses, the 5-year risks after CIN1 diagnosed in a single calendar year versus two consecutive calendar years were 4.3% versus 3.4% for CIN3+, 0.2% versus 0.1% for cervical cancer, and 15.4% versus 14.3% for CIN2+. Repeated CIN1 was not associated with higher subsequent CIN3+ risk, supporting conservative, risk-based follow-up after CIN1 biopsy.