title: [Order of twins--random choice of natural selection?].
abstract: OBJECTIVE
  Testing of hypothesis that the order of twins is random.
  
  
  METHODS
  Confrontation of birthweight and incidence of stillbirth between twins.
  
  
  METHODS
  The group of 829 twin deliveries was investigated. Probability of distribution was assessed according to Bernoullie's trials schema.
  
  
  RESULTS
  The first twin was usually heavier then the second one (p = 0.05), especially at term. Order of twin delivery was influenced by a birthweight difference > 250 g. In cases of single twin intrauterine death, the alive, term baby was delivered as the first one statistically more common (p = 0.029), despite of smaller number of cases. Discussion suggests that differences between twins are rather reasons of observed order than results.
  
  
  CONCLUSIONS
  Hypothesis of natural selection of stronger baby for the first delivery was presented.
authors.affiliation: Kliniki Perinatologii AM im. Karola Marcinkowskiego w Poznaniu.
authors.forename: Zbyszko
authors.initials: Z
authors.lastname: Malewski
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Seremak-Mrozikiewicz
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Drews
mesh_terms: D001722:Birth Order; D001724:Birth Weight; D036861:Delivery, Obstetric / Q000706:statistics & numerical data; D005260:Female; D005313:Fetal Death; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D011044:Poland / Q000453:epidemiology; D011247:Pregnancy; D011256:Pregnancy Outcome; D014427:Twins / Q000706:statistics & numerical data