A charity conducting government-funded research into incest is struggling to complete the project because not enough people are willing to discuss the subject.
The Department for Education and Skills pledged just under £100,000 to the Relationship Centre for the three-year study.
The charity, formerly known as Arc, has completed the first year of the research, which looks at the effects of incestuous relationships on women who become pregnant as a result, and their subsequent parenting abilities.
But Lucy Hughes, deputy director of services at the Relationship Centre, said it had been difficult to retain people because of the nature of the issues being dealt with.
"The problem is that it's almost the very last taboo," she said. "It's very difficult to get people to engage and to open up and talk about these issues because it is very much a secretive situation when it's happening."
The charity, which deals with unhealthy relationships, offers help through face-to-face, telephone or email counselling to anyone who comes forward.
The research was commissioned almost a decade after the Channel 4 soap Brookside caused controversy by introducing TV's first ever incest storyline, featuring brother and sister Nat and Georgia Simpson.
Disclosures from women in the charity's primary client group - victims of domestic violence - that they had also been victims of childhood sex abuse, led to the research.
Hughes added that the research is no longer being restricted solely to women. She said: "A number of men came through who have discovered that relationships with their children have been affected because they have not sorted out their own problems."