Objective The aims of this study were (i) to examine whether women referred for assessment of precancerous changes in the cervix had higher rates of preterm birth compared with those in the general population and (ii) to compare preterm birth rates for treated and untreated women adjusting for possible confounding factors.
Design Retrospective cohort design.
Setting Teaching hospital.
Population All women referred to the Royal Women’s Hospital, Melbourne (1982–2000), who subsequently had a birth recorded on the Victorian Perinatal Data Collection system (n= 5548).
Methods Record linkage of hospital dysplasia clinic records and population-based birth records.
Main outcome measures Total preterm delivery (<37 weeks of gestation) and subtypes.
Results Both treated and untreated women were at a significantly increased risk for preterm birth compared with those in the general population: treated—standardised prevalence ratio (SPR) 2.0, 95% CI 1.8–2.3 and untreated—SPR 1.5, 95% CI 1.4–1.7. Within the cohort, the treated women were significantly more likely to give birth preterm (adjusted OR 1.23, 95% CI 1.01–1.51). An increased risk of preterm birth was also associated with a history of induced or spontaneous abortions, illicit drug use during pregnancy or a major maternal medical condition. Cone biopsy, loop electrosurgical excision procedure and diathermy were associated with preterm birth. After adjusting for possible confounding factors, only diathermy remained significant (adjusted OR 1.72, 95% CI 1.36–2.17). Women treated using laser ablation were not at an increased risk for preterm birth (adjusted OR 1.1, 95% CI 0.8–1.4).
Conclusions Diagnosis of precancerous changes in the cervix (regardless of the treatment) was associated with an increased risk of preterm birth. Consideration should be given to the preferential use of ablative treatments.