title: Perinatal outcome of singletons and twins after assisted conception: a systematic review of controlled studies.
abstract: OBJECTIVE
  To compare the perinatal outcome of singleton and twin pregnancies between natural and assisted conceptions.
  
  
  METHODS
  Systematic review of controlled studies published 1985-2002.
  
  
  METHODS
  25 studies were included of which 17 had matched and 8 had non-matched controls.
  
  
  METHODS
  Very preterm birth, preterm birth, very low birth weight, low birth weight, small for gestational age, caesarean section, admission to neonatal intensive care unit, and perinatal mortality.
  
  
  RESULTS
  For singletons, studies with matched controls indicated a relative risk of 3.27 (95% confidence interval 2.03 to 5.28) for very preterm (< 32 weeks) and 2.04 (1.80 to 2.32) for preterm (< 37 weeks) birth in pregnancies after assisted conception. Relative risks were 3.00 (2.07 to 4.36) for very low birth weight (< 1500 g), 1.70 (1.50 to 1.92) for low birth weight (< 2500 g), 1.40 (1.15 to 1.71) for small for gestational age, 1.54 (1.44 to 1.66) for caesarean section, 1.27 (1.16 to 1.40) for admission to a neonatal intensive care unit, and 1.68 (1.11 to 2.55) for perinatal mortality. Results of the non-matched studies were similar. In matched studies of twin gestations, relative risks were 0.95 (0.78 to 1.15) for very preterm birth, 1.07 (1.02 to 1.13) for preterm birth, 0.89 (0.74 to 1.07) for very low birth weight, 1.03 (0.99 to 1.08) for low birth weight, 1.27 (0.97 to 1.65) for small for gestational age, 1.21 (1.11 to 1.32) for caesarean section, 1.05 (1.01 to 1.09) for admission to a neonatal intensive care unit, and 0.58 (0.44 to 0.77) for perinatal mortality. The non-matched studies mostly showed similar trends.
  
  
  CONCLUSIONS
  Singleton pregnancies from assisted reproduction have a significantly worse perinatal outcome than non-assisted singleton pregnancies, but this is less so for twin pregnancies. In twin pregnancies, perinatal mortality is about 40% lower after assisted compared with natural conception.
authors.affiliation: Department of Obstetrics, Gynaecology and Reproductive Medicine, Leiden University Medical Center, NL 2300 Leiden, Netherlands. f.m.helmerhorst@lumc.nl
authors.forename: Frans M
authors.initials: FM
authors.lastname: Helmerhorst
authors.forename: Denise A M
authors.initials: DA
authors.lastname: Perquin
authors.forename: Diane
authors.initials: D
authors.lastname: Donker
authors.forename: Marc J N C
authors.initials: MJ
authors.lastname: Keirse
mesh_terms: D001724:Birth Weight; D002585:Cesarean Section / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D007226:Infant Mortality; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age; D015931:Intensive Care, Neonatal / Q000706:statistics & numerical data; D007752:Obstetric Labor, Premature / Q000209:etiology; D011247:Pregnancy; D011256:Pregnancy Outcome; D011272:Pregnancy, Multiple / Q000706:statistics & numerical data*; D016032:Randomized Controlled Trials as Topic; D027724:Reproductive Techniques, Assisted / Q000009:adverse effects*; D014427:Twins / Q000706:statistics & numerical data