The pressure to perform when a woman is at her most fertile drives men away, a new study suggests.
The pressure of rigorously timed love making sessions spurred one in ten men surveyed to have an affair, and a quarter claimed it made them impotent.
More than 400 men took part in the study, which found the pressure to conceive a baby caused men acute stress.
Fertility experts tell couples to time sex with the window when a woman is ovulating. There are even devices designed to help couples work out - down to the minute - when a woman is at her most fertile.
But as the number of timed sex sessions increased so did the men's level of stress, according to the research carried out in South Korea. None of the men in the study had ever had sexual problems.