Desire was scored using an established model called the Female Sexual Function Index, which ranges from 1.2 to 6.0.
The participants reported being generally satisfied with their relationships and sex lives, but women reported lower levels of desire depending on the length of their relationship.
Knowing that many women's sexual desire diminishes over the course of a relationship could encourage both partners to be more realistic about their sex lives, and could help them weather the changes in desire as they occur.
Sex researchers Sarah Murray and Robin Milhausen, both of the University of Guelph in Ontario, Canada, asked 170 undergraduate women and men who had been in heterosexual relationships for anywhere from one month to nine years to report on their levels of relationship satisfaction, sexual satisfaction and sexual desire.
The researchers cautioned that longer-term studies of desire that include older couples could show different results.
Younger women may report decreased desire as they experience their first relationship move away from the "honeymoon phase," for example.
"Thus, it may be that men are not accurately reporting their level of desire and they may too experience a decrease." Murray is preparing to study whether men accurately report their levels of desire.
A few friends come over every Saturday, from noon to 8pm, to play videogames. And I think that makes her the perfect girl for me.
This is what happens at my house at least once a week. In fact, my girlfriend and I have almost no common interests.
The new research could also help couples manage their relationships over time.
In an earlier study, Murray found that women who reported more realistic expectations about what sex would be like in a long-term relationship also had higher levels of desire than those with less realistic expectations.