Genetic Factors and Variance in Fecundability: A Population-based Twin Study
Christensen, Kaare, Hans-Peter Kohler, Olga Basso, Jørn Olsen, James W. Vaupel, Joseph L. Rodgers
Abstract:
Background: A number of rare genetic conditions are known to influence fecundability in both males and females. It is less clear to which extent more subtle genetic differences influence fecundability on a population level.
Methods: In 1994 a population-based survey was conducted among Danish twins born 1953-1982. The response rate was 89%. Fecundability was assessed as the waiting time to pregnancy (WTP) at the first attempt to achieve a pregnancy.
Results: The WTP distribution for males was shifted slightly towards shorter WTP compared with females but there were no sex differences in intrapair similarity. We found a significant intrapair correlation in WTP for 645 monozygotic twin pairs (r = 0.22 (95% CI : [0.12; 0.32]), while there was no intrapair correlation for 826 same-sexed dizygotic twin pairs (r= 0.00 (95% CI:[(-0.09); 0.10]).
Conclusion: The significant correlation in WTP for monozygotic twins can be due to genetic factors although similarities in reporting behaviors cannot be ruled out as contributory to the correlation. Anyhow the lack of correlation in WTP for dizygotic twins indicates that possible genetic factors of importance for WTP are acting non-additively. Hence, identifying specific gene variants which influence fecundability on a population level may prove difficult due to gene-gene interactions.