title: Naturally conceived twins with monochorionic placentation have the highest risk of fetal loss.
abstract: OBJECTIVE
  The aim of this study was to estimate the rate of fetal loss in dichorionic (DC) and monochorionic (MC) twin pregnancies stratified according to zygosity and method of conception.
  
  
  METHODS
  In a prospective multicenter observational study women with a twin pregnancy had an ultrasound scan before 14 + 6 weeks' gestation in order to determine chorionicity. The fetal loss rate, the perinatal, neonatal and infant mortality rates and the frequency of very preterm labor were estimated for the different types of twin.
  
  
  RESULTS
  Among the 495 pregnancies (421 DC and 74 MC) 229 (46%) were conceived naturally and 266 (54%) by assisted reproduction (AR). Outcome data for 945 liveborn babies were obtained. The spontaneous miscarriage rate before 24 weeks' gestation was 10.9% (7/64) among naturally conceived MC compared to 3.0% (5/165) for naturally conceived DC twins (P < 0.05). For twins conceived by AR the corresponding figures were 0% (0/10) and 0.4% (1/256). The odds ratio (OR) for very preterm birth-before 28 weeks' gestation-was 4.2 for MC twins compared to DC twins. The relative risk of fetal loss or death among DC twins was 20% of the risk for MC twins.
  
  
  CONCLUSIONS
  The risk of fetal loss, very preterm delivery and neonatal/infant death is significantly higher among twins with MC compared to DC placentation. Twins conceived by AR have a much lower risk of MC placentation. The risk of losing one or both twins seems higher among naturally conceived twins compared to twins conceived by AR, despite the fact that the maternal age was higher among the mothers of the AR twins.
authors.affiliation: Department of Fetal, Maternal and Reproductive Medicine, Rigshospitalet, Denmark. lenesperling@dadlnet.dk
authors.forename: L
authors.initials: L
authors.lastname: Sperling
authors.forename: C
authors.initials: C
authors.lastname: Kiil
authors.forename: L U
authors.initials: LU
authors.lastname: Larsen
authors.forename: I
authors.initials: I
authors.lastname: Qvist
authors.forename: M
authors.initials: M
authors.lastname: Schwartz
authors.forename: C
authors.initials: C
authors.lastname: Jørgensen
authors.forename: K
authors.initials: K
authors.lastname: Skajaa
authors.forename: J
authors.initials: J
authors.lastname: Bang
authors.forename: A
authors.initials: A
authors.lastname: Tabor
mesh_terms: D000328:Adult; D001724:Birth Weight; D002823:Chorion; D005260:Female; D005313:Fetal Death / Q000209:etiology*; D006801:Humans; D007226:Infant Mortality; D007231:Infant, Newborn; D007234:Infant, Premature; D008297:Male; D008423:Maternal Age; D010929:Placentation; D011247:Pregnancy; D011256:Pregnancy Outcome; D011272:Pregnancy, Multiple; D011446:Prospective Studies; D027724:Reproductive Techniques, Assisted; D012307:Risk Factors; D014427:Twins; D016216:Ultrasonography, Prenatal