Associations between cervical intraepithelial neoplasia during pregnancy, previous excisional treatment, cone-length and preterm delivery: a register-based study from western Sweden

Abstract

Background: Excisional treatment of cervical intraepithelial neoplasia (CIN) has been associated with increased risk of preterm delivery (PTD), although the underlying mechanism is as yet unclear. Studies on formalin-fixed excised tissue indicate that the risk increases with cone-length, but the magnitude of increase is uncertain, especially in case of minor excisions (≤10 mm), as well compared to women with untreated CIN during pregnancy. This study assesses the impact of cone-length at previous treatment for CIN as well as diagnosis of CIN during pregnancy on the risk of PTD.

Methods: A register-based cohort study in western Sweden linking cervical cytology, histology, and treatment data from the Swedish National Cervical Screening Registry to data on obstetric outcomes in singleton pregnancies 2008-2016 from the Swedish Medical Birth Registry. These groups were compared for PTD and other obstetric outcomes: (1) women with one excisional treatment (n=3250, including a subgroup (n=2408) with cone-length measured before fixation; (2) women with untreated CIN diagnosed during pregnancy (n=1380); and (3) women with normal cytology (n=42,398). Logistic regression analyses were adjusted for socioeconomic and health-related confounders.

Results: Treated women had increased risk of PTD (adjusted odds ratio (aOR) 1.60, 95% confidence interval (CI) 1.21-2.12), spontaneous PTD (aOR 1.95, 95% CI 1.40-2.72) and preterm prelabor rupture of membranes (pPROM) (aOR 2.74, 95% CI 1.66-4.51) compared to the CIN during pregnancy group. ORs were similar when compared to the normal cytology group. Risks of these outcomes increased with cone-length. Mean cone-length was 9.1 mm. Cone-length ≤10 mm was associated with increased risk of PTD (aOR 1.41, 95% CI 1.02-1.94), spontaneous PTD (aOR 1.73, 95% CI 1.18-2.54), and pPROM (aOR 2.44, 95% CI 1.40-4.28), compared to the CIN during pregnancy group. The PTD risk was similar for cone-lengths 3-10 mm, thereafter increasing by 15% with each additional millimeter.

Conclusions: This study suggests that all excisional treatment, including small cones, are associated with increased risk of PTD and pPROM. Risks increase further with cone-length. In women of reproductive age, clinicians should aim to remove all CIN but minimal healthy cervical tissue. Cone-length should be recorded at treatment, for future prenatal risk estimation.

Keywords: Cervical intraepithelial neoplasia; Cone-length; Preterm delivery; Preterm prelabor rupture of the membranes.