Congenital malformations in twins: An international study

Pierpaolo Mastroiacovo, Eduardo E. Castilla, Carla Arpino, Beverley Botting, Guido Cocchi, Janine Goujard, Chiara Marinacci, Paul Merlob, Julia Métneki, Osvaldo Mutchinick, Annukka Ritvanen, Aldo Rosano

Research output: Article

137 Citations (Scopus)


Data provided by nine registries based in European and Latin America countries were analyzed to assess whether there is an excess of malformations in twins compared to singletons. Specific congenital malformations were coded according to the ninth revision of the International Classification of Diseases (ICD). Malformation rates and rate ratios (RR) for twins compared to singletons were calculated for each registry, and the homogeneity of the RRs was tested using the test of Breslow and Day. If departure from homogeneity in the different registries was not significant, registry-adjusted RRs with 95% confidence intervals were calculated. Overall, among 260,865 twins, 5,572 malformations were reported. A total of 101 different types of malformations or groups of defects was identified, and a homogeneous estimate of the RRs among registries was found for 91.1% of the malformations. Thirty-nine of the 92 malformations with homogeneous estimates of RRs were more common in twins than in singletons. For the remaining nine malformations, heterogeneous estimates of RRs were obtained. This study confirms the majority of already known associations and further identities previously unreported malformations associated with twins. In conclusion, there is an excess of malformations in twins compared with singletons, and all anatomical sites are involved. The number of specific malformations associated with twins is higher than that previously reported in smaller studies.

Original languageEnglish
Pages (from-to)117-124
Number of pages8
JournalAmerican journal of medical genetics
Issue number2
Publication statusPublished - márc. 12 1999

ASJC Scopus subject areas

  • Genetics
  • Genetics(clinical)

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    Mastroiacovo, P., Castilla, E. E., Arpino, C., Botting, B., Cocchi, G., Goujard, J., Marinacci, C., Merlob, P., Métneki, J., Mutchinick, O., Ritvanen, A., & Rosano, A. (1999). Congenital malformations in twins: An international study. American journal of medical genetics, 83(2), 117-124.<117::AID-AJMG7>3.0.CO;2-4