Risk of preterm delivery after excision of the cervical transformation zone

BackgroundCervical screening in the UK leads to ~50,000/year women having LLETZ (large loop excision of the transformation zone). Observational studies find an association between LLETZ and subsequent preterm delivery, but do not address whether the association is because LLETZ causes premature delivery or because women who require LLETZ are also more likely to have preterm deliveries. Preterm delivery produces a substantial emotional and economic burden, especially at Aims Compare preterm (and severely preterm) delivery rates in women who i) have undergone excision of the cervical transformation zone; ii) have been referred to colposcopy but only received a punch biopsy; and ii) received LLETZ AFTER pregnancy; to those in the entire English population To ascertain the association between preterm delivery and depth of cervical tissue removed to set guidelines regarding appropriate depth of excision to minimise prematurity To ascertain the association between other types of treatment for cervical disease (i.e. ablation, cryotherapy) and the risk of preterm delivery To investigate the relationship between the time from treatment to conception and the risk of preterm delivery to see whether the risk is limited to conceptions within 6 months of treatmentPlan of InvestigationThe study will collect colposcopy and cervical pathology data retrospectively from routine databases within the NHS and link these data to obstetric outcome using the HES database (Hospital Episode Statistics). To ensure that the study is time and cost efficient it will be carried out in three stages: 1) Collate NHS numbers only for biopsied women, 2) Link these NHS numbers to obstetric outcome in HES and select a sub sample of this population that has had a preterm delivery (cases) and the same number that had a term delivery (controls), 3) Send the selected sub sample of NHS numbers back to the treatment centres to obtain full treatment details. All identifying details will then be removed and submitted for analysis at a national level.Potential ImpactIt is unclear whether the observed association between CIN treatment and preterm delivery is due to the treatment, the CIN, or something about women who get CIN. We will compare women with different depths of excision and deliveries before and after treatment and will adjust for factors that increase the risk of both CIN and preterm delivery. This multi-centre study in the NHS Cervical Screening Programme will enable it to issue evidence-based guidance on the treatment of CIN (~50,000/year). Currently, conservative treatment means removing more not less tissue and women are not advised to avoid conception for a few months after treatment. This study could change practice regarding depth of cone and advice on time from treatment to conception so as to minimize the risk of preterm delivery.