title: Duration of second stage of labor and instrumental delivery as risk factors for severe perineal lacerations: population-based study.
abstract: BACKGROUND
  We sought to investigate the impact of the duration of second stage of labor on risk of severe perineal lacerations (third and fourth degree).
  
  
  METHODS
  This population based cohort study was conducted in the Stockholm/Gotland region, Sweden, 2008-2014. Study population included 52 211 primiparous women undergoing vaginal delivery with cephalic presentation at term. Unconditional logistic regression analysis was used to calculate crude and adjusted odds ratios (OR), using 95% confidence intervals (CI). Main exposure was duration of second stage of labor, and main outcome was risks of severe perineal lacerations (third and fourth degree).
  
  
  RESULTS
  Risk of severe perineal lacerations increased with duration of second stage of labor. Compared with a second stage of labor of 1 h or less, women with a second stage of more than 2 h had an increased risk (aOR 1.42; 95% CI 1.28-1.58). Compared with non-instrumental vaginal deliveries, the risk was elevated among instrumental vaginal deliveries (aOR 2.24; 95% CI 2.07-2.42). The risk of perineal laceration increased with duration of second stage of labor until less than 3 h in both instrumental and non-instrumental vaginal deliveries, but after 3 h, the ORs did not further increase. After adjustments for potential confounders, macrosomia (birth weight > 4 500 g) and occiput posterior fetal position were risk factors of severe perineal lacerations.
  
  
  CONCLUSIONS
  The risk of severe perineal laceration increases with duration until the third hour of second stage of labor. Instrumental delivery is the most significant risk factor for severe lacerations, followed by duration of second stage of labor, fetal size and occiput posterior fetal position.
authors.affiliation: Clinical Epidemiology Unit, T2, Department of Medicine Solna, Karolinska University Hospital and Institutet, Stockholm, SE 171 76, Sweden. marija.simic@ki.se.
authors.forename: Marija
authors.initials: M
authors.lastname: Simic
authors.affiliation: Clinical Epidemiology Unit, T2, Department of Medicine Solna, Karolinska University Hospital and Institutet, Stockholm, SE 171 76, Sweden.
authors.forename: Sven
authors.initials: S
authors.lastname: Cnattingius
authors.affiliation: Clinical Epidemiology Unit, T2, Department of Medicine Solna, Karolinska University Hospital and Institutet, Stockholm, SE 171 76, Sweden.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Petersson
authors.affiliation: Clinical Epidemiology Unit, T2, Department of Medicine Solna, Karolinska University Hospital and Institutet, Stockholm, SE 171 76, Sweden.|Department of Women's and Children's Health, Division of Obstetrics and Gynecology, Karolinska University Hospital and Institutet, Stockholm, SE-171 76, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Sandström
authors.affiliation: Clinical Epidemiology Unit, T2, Department of Medicine Solna, Karolinska University Hospital and Institutet, Stockholm, SE 171 76, Sweden.|Department of Women's and Children's Health, Division of Obstetrics and Gynecology, Karolinska University Hospital and Institutet, Stockholm, SE-171 76, Sweden.
authors.forename: Olof
authors.initials: O
authors.lastname: Stephansson
mesh_terms: D000328:Adult; D036861:Delivery, Obstetric / Q000009:adverse effects*; D004841:Episiotomy / Q000009:adverse effects* / Q000295:instrumentation; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D022125:Lacerations / Q000453:epidemiology* / Q000209:etiology; D008297:Male; D007744:Obstetric Labor Complications / Q000453:epidemiology* / Q000209:etiology; D009772:Obstetrical Forceps / Q000009:adverse effects*; D016017:Odds Ratio; D010502:Perineum / Q000293:injuries*; D011159:Population Surveillance; D011247:Pregnancy; D012189:Retrospective Studies; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult
keywords: Episiotomy; Instrumental delivery; Macrosomia; Obstetric anal sphincter injury; Occiput posterior position; Partograph; Perineal lacerations; Pregnancy; Second stage of labor