OBJECTIVE: To determine how the proportion of the cervical volume excised affects cervical regeneration.DESIGN: Prospective observational study.SETTING: University Hospital.POPULATION: Women planning to undergo excisional treatment for cervical intraepithelial neoplasia who wish to have future pregnancies.METHODS: The cervical volume (and dimensions) is calculated with magnetic resonance imaging (MRI) before treatment. The volume (and dimensions) of the cone is assessed before fixation by a volumetric tube and a ruler; the percentage (%) of excision is computed. Cervical regeneration is estimated by repeat MRI at 6 months.MAIN OUTCOME MEASURES: Cervical regeneration in relation to proportion of excision. Statistical analysis was performed by box plots and analysis of variance.RESULTS: A total of 48 women have been recruited; 29 have completed 6 months follow up. Both the total cervical volume (from MRI) before treatment and the volume of the excised/ablated cone varied substantially. The estimated proportion of excision varied significantly between 4% and 39% (median 11%). Multivariate linear regression revealed that the proportional deficit at 6 months post-treatment was determined mainly by the proportion of the excised volume.CONCLUSIONS: Careful assessment of risks and benefits of treatment is essential when deciding to treat women who wish to have future pregnancies. Assessment of the proportion of the cervical volume and length excised might identify those that need further surveillance during future pregnancy.