title: Induced Labor in Sweden, 1999-2012: A Population-Based Cohort Study.
abstract: Previous studies show contradictory results about the impact of induced labor on the cesarean delivery rate and few studies have investigated the risk of vacuum extraction subsequent to induced labor. The aims of the present study were to describe the rate of induced labor in Sweden from 1999 to 2012, and to assess the risk of unplanned cesarean delivery and vacuum extraction after induced labor in relation to medical complications and length of gestation.
  
  
  
  A register-based cohort study was conducted, including 1,078,536 women with spontaneous or induced onset of labor who gave birth by noninstrumental vaginal delivery, unplanned cesarean delivery, or vacuum extraction in gestational week 37 + 0 to 41 + 6. Logistic regression was used to study the association between induced labor and instrumental delivery.
  
  
  
  The rate of induced labor increased from 7.7 to 12.9 percent among primiparous and from 7.5 to 11.8 percent among multiparous women. Induced labor was associated with 2-3 times greater risk of unplanned cesarean delivery among all women, except multiparas in gestational week 37-38, and with a 20-50 percent higher risk of vacuum extraction after the adjustment for confounding factors. Among women without a recognized medical complication, induced labor was associated with a threefold increased risk of cesarean delivery in gestational week 39-41 and a 40 percent increase in gestational week 37-38 compared with women with spontaneous onset of labor.
  
  
  
  The proportion of induced labors increased substantially during the 14-year study period and was associated with an increased risk of both cesarean delivery and vacuum extraction, even in women without a documented medical complication. The increased risk of instrumental delivery should be taken into account when counseling about the risks and benefits of induced labor.
authors.affiliation: Department of Women's and Children's Health, Division of Reproductive Health, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Ekéus
authors.affiliation: Department of Women's and Children's Health, Division of Reproductive Health, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Helena
authors.initials: H
authors.lastname: Lindgren
mesh_terms: D000293:Adolescent; D000328:Adult; D002585:Cesarean Section / Q000706:statistics & numerical data*; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007745:Labor Onset; D007751:Labor, Induced / Q000639:trends*; D016015:Logistic Models; D008423:Maternal Age; D008875:Middle Aged; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology*; D012042:Registries; D013548:Sweden / Q000453:epidemiology; D014620:Vacuum Extraction, Obstetrical / Q000009:adverse effects*; D055815:Young Adult
keywords: cesarean delivery; epidemiology; induced labor; mode of delivery; vacuum extraction