title: Assisted fertilization and breech delivery: risks and obstetric management.
abstract: BACKGROUND
  Previous studies have suggested that assisted reproduction technology (ART) is associated with increased risk of breech presentation. We investigated whether factors that tend to differ between ART and spontaneously conceived pregnancies may explain the higher risk of breech deliveries associated with ART.
  
  
  METHODS
  In this population-based cohort study, we included 1 209 151 singleton pregnancies reported to the Medical Birth Registry of Norway between 1984 and 2006 and compared the risk of breech presentation in 8229 ART pregnancies with that in spontaneously conceived pregnancies. Risk ratios (RR), adjusted for maternal age, parity, gestational length and year of birth, were estimated using binominal regression, and we describe differences and time trends in obstetric management for breech and cephalic presentations after ART compared with management of spontaneously conceived pregnancies.
  
  
  RESULTS
  Breech presentation occurred nearly 50% more often in ART singleton pregnancies than in spontaneously conceived singletons [crude RR: 1.48, 95% confidence interval (CI): 1.34-1.64], but after adjustment for potentially confounding factors, the difference was fully attenuated (RR: 0.97, 95% CI: 0.88-1.07). The most important contributors to the attenuation were parity and length of gestation. In general, Caesarean sections and induced deliveries were more likely in ART pregnancies, but over the study period, the proportion of Caesarean sections in ART pregnancies gradually approached that of spontaneously conceived pregnancies.
  
  
  CONCLUSIONS
  Increased risk of breech presentation in pregnancies after ART is mediated by lower parity and shorter gestational length. In general, the obstetric management of women with ART pregnancies is gradually approaching the ordinary surveillance of pregnant women.
authors.affiliation: Department of Obstetrics and Gynaecology, IVF Unit, St Olav's University Hospital, Trondheim NO-7006, Trondheim, Norway. libero@ntnu.no
authors.forename: Liv Bente
authors.initials: LB
authors.lastname: Romundstad
authors.forename: Pål R
authors.initials: PR
authors.lastname: Romundstad
authors.forename: Arne
authors.initials: A
authors.lastname: Sunde
authors.forename: Vidar
authors.initials: V
authors.lastname: von Düring
authors.forename: Rolv
authors.initials: R
authors.lastname: Skjaerven
authors.forename: Lars J
authors.initials: LJ
authors.lastname: Vatten
mesh_terms: D000328:Adult; D001946:Breech Presentation / Q000209:etiology*; D002585:Cesarean Section / Q000706:statistics & numerical data / Q000639:trends; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008423:Maternal Age; D010298:Parity; D011247:Pregnancy; D012042:Registries; D027724:Reproductive Techniques, Assisted / Q000009:adverse effects*; D012306:Risk; D055815:Young Adult