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.

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.