Heritability of subfertility among Danish twins

The results from two large population-based studies of Danish twins suggest that environmental factors specific for each twin individual explain around 70% of the subfertility in females and around 95% of that in males.

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VOLUME 114, ISSUE 3, P618-627


Linda Juel Ahrenfeldt, Ph.D., Sören Möller, Ph.D., Maarten Wensink, Ph.D., Tina Kold Jensen, Ph.D., Kaare Christensen, M.D., Ph.D., Rune Lindahl-Jacobsen, Ph.D.



To investigate the relative contribution of genetic and environmental components to subfertility.


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.


Not applicable.


A total of 9053 Danish monozygotic and dizygotic same-sex twins aged 18+ years from nationwide twin surveys (twins born 1931−1976).


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.


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.


Unique environmental factors explain most of the observed variation in subfertility, when measured as waiting time to pregnancy.

Fertility and Sterility

Editorial Office, American Society for Reproductive Medicine

Fertility and Sterility® is an international journal for obstetricians, gynecologists, reproductive endocrinologists, urologists, basic scientists and others who treat and investigate problems of infertility and human reproductive disorders.