Differences and similarities in the intra-uterine behaviour of monozygotic and dizygotic twins

Alessandra Piontelli, Luisa Bocconi, Chiara Boschetto, Alessandra Kustermann, Umberto Nicolini

Research output: Contribution to journalArticlepeer-review


Diagnostic advances have made it possible to use ultrasonograph to assess placentation and therefore zygosity in utero in the case of monochorionic-monozygotic twins. Foetal behaviour of 15 monozygotic and 15 unlike-sexed dizygotic twin pairs was studied serially with ultrasounds from 10 to 22 weeks gestational age. Each twin, regardless of its zygosity, showed individualised behavioural styles. One twin was found to be 'dominant' in the sense of being more active, but less reactive, possibly due to the fewer stimuli being generated by its co-twin. Monozygotic twins, as opposed to dizygotic twins, showed greater similarities in activity and reactivity levels, but were never behaviourally identical and decreased in likeness with increasing age. Our data suggest that so-called identical twins are very similar, but not behaviourally identical, from very early in pregnancy. The unequally shared intrauterine environment contributes to putting each monozygotic twin on a progressively distinct behavioural path.

Original languageEnglish
Pages (from-to)264-273
Number of pages10
JournalTwin Research
Issue number4
Publication statusPublished - Dec 1999


  • Dizygotic twins
  • Foetal behaviour
  • Monozygotic twins
  • Twins' individual consistencies
  • Twins' intra-pair differences

ASJC Scopus subject areas

  • Genetics(clinical)
  • Pediatrics, Perinatology, and Child Health
  • Obstetrics and Gynaecology


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