Abstract
The Colorado Twin Registry is a population based registry initiated in 1984 with the involvement of the Colorado Department of Health, Division of Vital Statistics. Recruitment includes birth cohorts several years prior to 1984 and all subsequent years. As part of a recent evaluation of Colorado birth records for the years 2006 through 2008 we became aware of a shifting trend in the proportion of MZ and DZ twins in the Colorado population. Historically (Bulmer 1970 The biology of twinning in man, Clarendon, Oxford) we have expected a 1/3, 1/3, 1/3 ratio of MZ, same-sex DZ and opposite sex DZ twins in Caucasian populations. An excess of MZ pairs in most studies was assumed to be due to selection bias. Somewhat more recently, Hur et al.(1995 Behav Genet 25, 337–340) provided evidence that the DZ twinning rate was falling and that therefore selection bias was not the reason for higher MZ enrollment in most twin studies. They suggested that twin researchers might consider strategies to over-enroll DZ pairs to maximize statistical power. In contrast, we now find that of the 3217 twin births in Colorado from 2006 to 2008 with identified sex information the MZ rate is estimated at only 22%, and we have corroborating reports from other states of similar estimates. These were calculated applying Weinberg’s rule which assumes an equal birth rate for same sex and opposite sex DZ pairs so that the proportion of MZ in a sample is the proportion of same sex (MM + FF) minus the proportion of opposite-sex (MF, FM). We explore factors, such as an increase in the proportion of non-Caucasian parents and an increase in average maternal age, which may contribute to this shift.
References
Bulmer MG (1970) The biology of twinning in man. Clarendon, Oxford
Hur Y-M, McGue M, Iacono WG (1995) Unequal rate of monozygotic and like-sex dizygotic twin birth: evidence from the minnesota twin family study. Behav Genet 25(4):337–340
Lykken DT, McGue M, Tellegen A (1987) Recruitment bias in twin research: the rule of two-thirds reconsidered. Behav Genet 17(4):343–361
Martin, JA, Hamilton BE, Osterman JK (2012) Three decades of twin births in the United States, 1980–2009. NCHS Data Brief No. 80. US Dept. of Health and Human Services, Centers for Disease Control and Prevention, National Center for Health Statistics.
Rhea SA, Gross AA, Haberstick BC, Corley RP (2006) Colorado twin registry. Twin Res Hum Genet 9:941–949
Rhea SA, Gross A, Haberstick BC, Corley RP (2013) Colorado twin registry: an update. Twin Res Hum Genet 16:351–357
Acknowledgements
We are grateful to the Departments of Health of the States of Colorado, Missouri, Minnesota, Virginia and North Carolina as well as to Rade Todorovich at Washington University in Missouri, Kevin P. Haroian at the University of Minnesota, and Judy Silberg and her assistants Emily Lilley and Anne Taylor-Morris at Virginia Commonwealth University for providing the comparative birth record data used in our analyses. The data sets were obtained from anonymous public sources (Departments of Health birth records).
Funding
The study was funded by NIH grants U01DA041120 and AA023974.
Author information
Authors and Affiliations
Corresponding author
Ethics declarations
Conflict of interest
Sally Ann Rhea, Robin P. Corley, Andrew C. Heath, William G. Iacono, Michael C. Neale and John K. Hewitt declare that they have no conflicts of interest.
Human and animal rights
This article does not contain any studies with human participants or animals performed by any of the authors.
Additional information
Edited by John K Hewitt.
Rights and permissions
About this article
Cite this article
Rhea, S.A., Corley, R.P., Heath, A.C. et al. Higher Rates of DZ Twinning in a Twenty-First Century Birth Cohort. Behav Genet 47, 581–584 (2017). https://doi.org/10.1007/s10519-017-9855-1
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10519-017-9855-1