Background Excisional procedures of cervical intraepithelial neoplasia (CIN) may increase the risk of preterm birth. It is unknown whether this increased risk is due to the excision procedure itself, to the underlying CIN, or to secondary risk factors that are associated with both preterm birth and CIN. The aim of this study is to assess the risk of spontaneous preterm birth in women with treated and untreated CIN and examine possible associations by making a distinction between the excised volume of cervical tissue and having cervical disease. Methods and findings This Dutch population-based observational cohort study identified women aged 29 to 41 years with CIN between 2005 and 2015 from the Dutch pathology registry (PALGA) and frequency matched them with a control group without any cervical abnormality based on age at and year of pathology outcome (i.e., CIN or normal cytology) and urbanization (= 100,000 inhabitants). All their 45,259 subsequent singleton pregnancies with a gestational age >= 16 weeks between 2010 and 2017 were identified from the Dutch perinatal database (Perined). Nineteen potential confounders for preterm birth were identified. Adjusted odds ratios (ORs) were calculated for preterm birth comparing the 3 different groups of women: (1) women without CIN diagnosis; (2) women with untreated CIN; and (3) women with treated CIN prior to each childbirth. In total, 29,907, 5,940, and 9,412 pregnancies were included in the control, untreated CIN, and treated CIN group, respectively. The control group showed a 4.8% (1,002/20,969) proportion of spontaneous preterm birth, which increased to 6.9% (271/3,940) in the untreated CIN group, 9.5% (600/6,315) in the treated CIN group, and 15.6% (50/321) in the group with multiple treatments. Women with untreated CIN had a 1.38 times greater odds of preterm birth compared to women without CIN (95% confidence interval (CI) 1.19 to 1.60; P < 0.001). For women with treated CIN, these odds 2.07 times increased compared to the control group (95% CI 1.85 to ...