title: Trends in perinatal health after assisted reproduction: a Nordic study from the CoNARTaS group.
abstract: OBJECTIVE
  Has the perinatal outcome of children conceived after assisted reproductive technology (ART) improved over time?
  
  
  CONCLUSIONS
  The perinatal outcomes in children born after ART have improved over the last 20 years, mainly due to the reduction of multiple births.
  
  
  BACKGROUND
  A Swedish study has shown a reduction in unwanted outcomes over time in children conceived after ART. Our analyses based on data from more than 92 000 ART children born in four Nordic countries confirm these findings.
  
  
  METHODS
  Nordic population-based matched cohort study with ART outcome and health data from Denmark, Finland, Norway and Sweden.
  
  
  METHODS
  We analysed the perinatal outcome of 62 379 ART singletons and 29 758 ART twins, born from 1988 to 2007 in four Nordic countries. The ART singletons were compared with a control group of 362 215 spontaneously conceived singletons. Twins conceived after ART were compared with all spontaneously conceived twins (n = 122 763) born in the Nordic countries during the study period. The rates of several adverse perinatal outcomes were stratified into the time periods: 1988-1992; 1993-1997; 1998-2002 and 2003-2007 and presented according to multiplicity.
  
  
  RESULTS
  For singletons conceived after ART, a remarkable decline in the risk of being born preterm and very preterm was observed. The proportion of ART singletons born with a low and very low birthweight also decreased. Finally, the stillbirth and infant death rates have declined among both ART singletons and twins. Throughout the 20 year period, fewer ART twins were stillborn or died during the first year of life compared with spontaneously conceived twins, presumably due to the lower proportion of monozygotic twins among the ART twins.
  
  
  CONCLUSIONS
  We were not able to adjust for some potential confounders such as BMI, smoking, length or cause of infertility. The Nordic ART populations have changed over time, and in recent years, both less as well as severely reproductive ill couples are being treated. This may have affected the observed trends.
  
  
  CONCLUSIONS
  It is assuring that data from four countries confirm an overall improvement over time in the perinatal outcomes of children conceived after ART. Furthermore, data show the beneficial effect of single embryo transfer, not only in regard to lowering the rate of multiples but also concerning the health of singletons.
  
  
  BACKGROUND
  The European Society for Human Reproduction and Embryology (ESHRE), the University of Copenhagen and the Danish Agency for Science, Technology and Innovation has supported the project. The CoNARTaS group has received travel and meeting funding from the Nordic Federation of Obstetrics and Gynecology (NFOG). None of the authors has any competing interests to declare.
authors.affiliation: Fertility Clinic, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark anna-karina.aaris.henningsen@rh.regionh.dk.
authors.forename: A A
authors.initials: AA
authors.lastname: Henningsen
authors.affiliation: THL, National Institute for Health and Welfare, Helsinki, Finland Nordic School of Public Health, Gothenburg, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Gissler
authors.affiliation: Department of Global Public Health and Primary Health Care, University of Bergen, Bergen, Norway Medical Birth Registry of Norway, Norwegian Institute of Public Health, Bergen, Norway.
authors.forename: R
authors.initials: R
authors.lastname: Skjaerven
authors.affiliation: Department of Obstetrics and Gynaecology, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden Reproductive Medicine, Sahlgrenska University Hospital, Gothenburg, Sweden.
authors.forename: C
authors.initials: C
authors.lastname: Bergh
authors.affiliation: Department of Obstetrics and Gynecology, Helsinki University Central Hospital, University of Helsinki, Helsinki, Finland.
authors.forename: A
authors.initials: A
authors.lastname: Tiitinen
authors.affiliation: Department of Obstetrics and Gynecology, Fertility Clinic, St Olav's University Hospital, Trondheim, Norway Department of Public Health, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: L B
authors.initials: LB
authors.lastname: Romundstad
authors.affiliation: Perinatal Centre, Department of Obstetrics and Gynecology, Institute for Clinical Sciences, Sahlgrenska Academy, Gothenburg, Sweden.
authors.forename: U B
authors.initials: UB
authors.lastname: Wennerholm
authors.affiliation: Gynecological Clinic, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark.
authors.forename: O
authors.initials: O
authors.lastname: Lidegaard
authors.affiliation: Fertility Clinic, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark.
authors.forename: A
authors.initials: A
authors.lastname: Nyboe Andersen
authors.affiliation: Department of Biostatistics, University of Copenhagen, Copenhagen, Denmark.
authors.forename: J L
authors.initials: JL
authors.lastname: Forman
authors.affiliation: Department of Obstetrics and Gynecology, Hvidovre Hospital, University of Copenhagen, Copenhagen, Denmark.
authors.forename: A
authors.initials: A
authors.lastname: Pinborg
mesh_terms: D015331:Cohort Studies; D005260:Female; D006801:Humans; D011247:Pregnancy; D011256:Pregnancy Outcome; D059285:Pregnancy, Twin / Q000706:statistics & numerical data; D027724:Reproductive Techniques, Assisted / Q000706:statistics & numerical data*; D012537:Scandinavian and Nordic Countries
keywords: assisted reproductive technology; preterm birth; small for gestational age; trends