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Malformations in Twins and Their Siblings, Norway, 1967-79

Published online by Cambridge University Press:  01 August 2014

G.C. Windham  and
T. Bjerkedal
G.C. Windham
Affiliation:
Medical Birth Registry of Norway, Norwegian Health Services, Department of Social Affairs, Oslo
T. Bjerkedal*
Affiliation:
Medical Birth Registry of Norway, Norwegian Health Services, Department of Social Affairs, Oslo
*
Medical Birth Registry, Institute of Preventive Medicine, University of Oslo, Gydas vei 8, Oslo, Norway

Abstract

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During 1967-79 the population-based Medical Birth Registry of Norway registered 7,660 twin pairs (1% of births) born to 7,596 mothers, who gave birth to 6,608 additional infants (twin siblings). The total rate of malformations among twins (278.1/10,000) was not significantly different than among singletons (302.1/10,000), nor among twin siblings (314.8/10,000). By specific type of defect, twins had significantly higher rates than singletons of central nervous system (CNS) defects (Rate Ratio = 1.8) and cardiovascular defects (RR = 1.5). The twins also had a significantly low rate of congenital hip dislocation (RR = 0.4), which may explain the relatively low incidence of malformations in twins. Like-sex (LS) twins had a slightly higher rate of malformations than unlike-sex (US) twins (RR = 1.1), as well as a higher rate of CNS defects (RR = 3.0). The siblings also had a significantly increased rate of CNS defects compared to singletons (RR = 1.9), but not of cardiovascular defects (RR = 0.9). The results indicate that twins have elevated rates of at least some congenital malformations. The observations about CNS defects suggest common factors that can lead to either like-sex twinning, CNS defects, or both. The increased frequency of cardiovascular defects in twins appears to be associated with the biologic conditions of twinning.

Keywords

TwinningCongenital malformationsAscertainment
Type
Research Article
Information
Acta geneticae medicae et gemellologiae: twin research , Volume 33 , Issue 1 , January 1984 , pp. 87 - 95
Copyright
Copyright © The International Society for Twin Studies 1984

References

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