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Month of Birth by Zygosity in the NAS-NRC Twin Registry

Published online by Cambridge University Press:  01 August 2014

Kenneth S. Kendler*
Affiliation:
Department of Psychiatry and Schizophrenia Biologic Research Center, Bronx Veterans Administration Medical Center, andMt. Sinai School of Medicine, Bronx, New York
C. Dennis Robinette
Affiliation:
Medical Follow-up Agency, National Academy of Sciences-National Research Council, Washington, DC
*
Department of Psychiatry, Bronx VA Medical Center, 130 West Kingsbridge Road, Bronx, NY 10468, USA

Abstract

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Previous results regarding a seasonality of twin births have been conflicting. Since the biology of monozygotic (MZ) twinning differs from that of dizygotic (DZ) twinning, it is possible that the seasonality of birth for these two twin types might differ. However, all previous studies examining the seasonality of birth by zygosity has estimated zygosity by Weinberg's method. In this report, the month of birth of all MZ and DZ veteran twins from the United States National Academy of Sciences-National Research Council (NAS-NRC) Twin Registry are compared with that found for an unselected group of veterans. Zygosity in the registry has been individually assigned to all twin pairs by a well-validated method. Compared to unselected veterans, the distribution of births by months did not differ significantly for all the veteran twin pairs or for the MZ and DZ twin pairs considered separately. The distribution of month of birth of the MZ and DZ twin pairs did not differ significantly from one another. These results are not consistent with a significant seasonality of MZ, DZ, or all twin births in the United States.

Type
Research Article
Copyright
Copyright © The International Society for Twin Studies 1983

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