Purpose A previous cervical intraepithelial neoplasia is associated with an increased obstetrical risk. It was the aim of the study to identify risk factors of preterm birth in patients with cervical intraepithelial neoplasia in dependence of the treatment modality (excisional vs. ablative). Methods Women with treated cervical intraepithelial neoplasia and subsequent pregnancy (n = 155) were included in this retrospective study. Methods of treatment were either conization by large loop excision of the transformation zone (LLETZ) or ablative laser vaporization. Results Of the total population 60.6% (n = 94) had a conization and 39.4% (n = 61) a laser vaporization alone. The frequency of preterm birth < 37 weeks was 9.7% (n = 15) without differences between conization and laser (11.7 vs. 6.7%, p = 0.407) with an odds ratio (OR) of 1.9 (95% confidence interval [CI] 0.6–6.2). Preterm birth < 34 weeks was found in 2.6% (n = 4), of which all had a conization (4.3 vs. 0%, p = 0.157). Risk factors for preterm birth were repeated cervical intervention (OR 4.7 [95% CI 1.5–14.3]), especially a combination of conization and laser ablation (OR 14.9 [95% CI 4.0–55.6]), age at intervention < 30 years (OR 6.0 [95% CI 1.3–27.4]), a history of preterm birth (OR 4.7 [95% CI 1.3–17.6]) and age at delivery < 28 years (OR 4.7 [95% CI 1.5–14.3]). Conclusion The large loop excision of the transformation zone as a modern, less invasive ablative treatment did not obviously increase the risk of preterm birth compared to laser vaporization. The most important risk factor for preterm delivery was the need of a repeated intervention, especially at younger age. We assume that the persistence or recurrence of the cervical intraepithelial neoplasia following a high-risk human papillomavirus infection is mainly responsible for the observed effect.