title: Cold-knife conisation and large loop excision of transformation zone significantly increase the risk for spontaneous preterm birth: a population-based cohort study.
abstract: OBJECTIVE
  Our aim was to explore the association between cold-knife conisation and large loop excision of transformation zone (LLETZ) with spontaneous preterm birth in a large 10-year national sample. We wanted to explore further the association of these procedures with preterm birth according to gestation.
  
  
  METHODS
  We conducted a population based retrospective cohort study, using data from national Medical Birth Registry. The study population consisted of all women giving birth to singletons in the period 2003-2012 in Slovenia, excluding all induced labors and elective cesarean sections before 37 weeks of gestation (N=192730). We compared the prevalence of spontaneous preterm births (before 28 weeks, before 32 weeks, before 34 weeks and before 37 weeks of gestation) in women with cold-knife conisation or LLETZ compared to women without history of conisation, calculating odds ratios (OR), adjusted for potential confounders. Chi-square test was used for descriptive analysis. Logistic regression analyses were performed to estimate crude odds ratio (OR) and adjusted odds ratio (aOR) and their 95% confidence intervals (95% CI) with two-sided probability (p) values.
  
  
  RESULTS
  A total of 8420 (4.4%) women had a preterm birth before 37 weeks of gestation, 2250 (1.2%) before 34 weeks of gestation, 1333 (0.7%) before 32 weeks of gestation and 603 (0.3%) before 28 weeks of gestation. A total of 4580 (2.4%) women had some type of conisation in their medical history: 2083 (1.1%) had cold-knife conisation and 2498 (1.3%) had LLETZ. In women with history of cold-knife conisation, the adjusted OR for preterm birth before 37 weeks of gestation was 3.13 (95% CI; 2.74-3.57) and for preterm birth before 28 weeks of gestation 5.96 (95% CI; 4.3-8.3). In women with history of LLETZ, the adjusted OR was 1.95 (95% CI; 1.68-2.25) and 2.88 (95% CI; 1.87-4.43), respectively.
  
  
  CONCLUSIONS
  Women with cervical excision procedure of any kind have significantly increased odds for preterm birth, especially for preterm birth before 28 weeks and before 32 weeks of gestation.
authors.affiliation: Department of Human Reproduction, Division of Obstetrics and Gynaecology, University Medical Centre Ljubljana, Slovenia. Electronic address: nina.jancar@kclj.si.
authors.forename: Nina
authors.initials: N
authors.lastname: Jančar
authors.affiliation: Health Survey and Health Promotion Department, National Institute of Public Health, Ljubljana, Slovenia.
authors.forename: Barbara
authors.initials: B
authors.lastname: Mihevc Ponikvar
authors.affiliation: Health Survey and Health Promotion Department, National Institute of Public Health, Ljubljana, Slovenia.
authors.forename: Sonja
authors.initials: S
authors.lastname: Tomšič
mesh_terms: D000293:Adolescent; D000328:Adult; D002584:Cervix Uteri / Q000601:surgery*; D019092:Conization / Q000009:adverse effects* / Q000379:methods; D005260:Female; D005865:Gestational Age; D006801:Humans; D015994:Incidence; D007231:Infant, Newborn; D008875:Middle Aged; D007752:Obstetric Labor, Premature / Q000453:epidemiology / Q000209:etiology*; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology / Q000209:etiology*; D012189:Retrospective Studies; D012306:Risk; D017524:Slovenia; D002583:Uterine Cervical Neoplasms / Q000601:surgery; D055815:Young Adult; D002578:Uterine Cervical Dysplasia / Q000601:surgery
keywords: Cervical intraepithelial neoplasia; Cold-knife conisation; Gestation; Large loop excision of transformation zone; Preterm birth