Heritability of subfertility among Danish twins
Linda Juel Ahrenfeldt1, Sören Möller2, Maarten Wensink3
1Unit of Epidemiology, Biostatistics and Biodemography, Department of Public Health, University of Southern Denmark, Odense, Denmark; The Danish Twin Registry, Department of Public Health, University of Southern Denmark, Odense, Denmark.
Objective:
To investigate the relative contribution of genetic and environmental components to subfertility.
Design:
Twin design using a quantitative genetic liability threshold model that splits the variation of subfertility into additive genetic effects, common environmental effects, and unique environmental effects.
Setting:
Not applicable.
Patients:
A total of 9053 Danish monozygotic and dizygotic same-sex twins aged 18+ years from nationwide twin surveys (twins born 1931-1976).
Intervention:
Not applicable.
Main Outcome Measures:
Time to pregnancy (TTP) restricted to first pregnancy as a binary outcome, with a cut-off point of 10 months.
Results:
Based on the Akaike information criterion, a model including additive genetic and unique environmental factors resulted in the best model fit. For females, the relative contribution of additive genetic factors to TTP was 28% (95% confidence interval [CI] 15%, 41%), whereas unique environmental factors explained 72% (95% CI 59%, 85%). For males, additive genetic factors explained 4% (95% CI 0%, 22%) of the variation in TTP, while unique environmental factors accounted for 96% (95% CI 78%, 100%). Results were overall similar for the crude model and consistent across surveys.
Conclusion:
Unique environmental factors explain most of the observed variation in subfertility, when measured as waiting time to pregnancy.
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