title: Exercise during pregnancy and risk of cesarean delivery in nulliparous women: a large population-based cohort study.
abstract: BACKGROUND
  Vaginal delivery for the first birth is of great importance for further obstetric performance for the individual woman. Given the rising cesarean delivery rates worldwide over the past decades, a search for modifiable factors that are associated with cesarean delivery is needed. Exercise may be a modifiable factor that is associated with type of delivery, but the results of previous studies are not conclusive.
  
  
  OBJECTIVE
  The purpose of this study was to investigate the association between exercise during pregnancy and cesarean delivery, both acute and elective, in nulliparous women.
  
  
  METHODS
  We conducted a population-based cohort study that involved 39,187 nulliparous women with a singleton pregnancy who were enrolled in the Norwegian Mother and Child Cohort Study between 2000 and 2009. All women answered 2 questionnaires in pregnancy weeks 17 and 30. Acute and elective cesarean delivery data were obtained from the Medical Birth Registry of Norway. Information on exercise frequency and type was assessed prospectively by questionnaires in pregnancy weeks 17 and 30. Generalized linear models estimated risk differences of acute and elective cesarean delivery for different frequencies and types of exercise during pregnancy weeks 17 and 30. We used restricted cubic splines to examine dose-response associations of exercise frequency and acute cesarean delivery. A test for nonlinearity was also conducted.
  
  
  RESULTS
  The total cesarean delivery rate was 15.4% (n=6030), of which 77.8% (n=4689) was acute cesarean delivery. Exercise during pregnancy was associated with a reduced risk of cesarean delivery, particularly for acute cesarean delivery. A nonlinear association was observed for exercise frequency in weeks 17 and 30 and risk of acute cesarean delivery (test for nonlinearity, P=.003 and P=.027, respectively). The largest risk reduction was observed for acute cesarean delivery among women who exercised >5 times weekly during weeks 17 (-2.2%) and 30 (-3.6%) compared with nonexercisers (test for trend, P<.001). Reporting high impact exercises in weeks 17 and 30 was associated with the greatest reduction in risk of acute cesarean delivery (-3.0% and -3.4%, respectively).
  
  
  CONCLUSIONS
  Compared with nonexercisers, regular exercise and high-impact exercises during pregnancy are associated with reduced risk of having an acute cesarean delivery in first-time mothers.
authors.affiliation: Norwegian National Advisory Unit on Women's Health, Department of Obstetrics and Gynaecology, Oslo University Hospital, Rikshospitalet, Oslo, Norway; Domain of Mental and Physical Health, Norwegian Institute of Public Health, Oslo, Norway. Electronic address: Katrine.Mari.Owe@fhi.no.
authors.forename: Katrine Mari
authors.initials: KM
authors.lastname: Owe
authors.affiliation: Domain of Mental and Physical Health, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Wenche
authors.initials: W
authors.lastname: Nystad
authors.affiliation: Domain of Mental and Physical Health, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Hein
authors.initials: H
authors.lastname: Stigum
authors.affiliation: Norwegian National Advisory Unit on Women's Health, Department of Obstetrics and Gynaecology, Oslo University Hospital, Rikshospitalet, Oslo, Norway; Domain of Mental and Physical Health, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Siri
authors.initials: S
authors.lastname: Vangen
authors.affiliation: Department of Sports Medicine, Norwegian School of Sport Sciences, Oslo, Norway.
authors.forename: Kari
authors.initials: K
authors.lastname: Bø
mesh_terms: D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D002585:Cesarean Section / Q000706:statistics & numerical data*; D015331:Cohort Studies; D017558:Elective Surgical Procedures / Q000706:statistics & numerical data; D004630:Emergencies; D015444:Exercise; D005260:Female; D006801:Humans; D008875:Middle Aged; D009664:Norway; D010298:Parity; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D011446:Prospective Studies; D065840:Protective Factors; D011795:Surveys and Questionnaires; D016474:Weight-Bearing; D055815:Young Adult
keywords: MoBa; mode of delivery; physical activity; pregnancy; risk difference