A researcher has suggested that it is "crucial" to put effort into keeping things "fun and interesting" in the bedroom as women's sex drives gradually ebb over time.
However, it is found that men's sex drive stays as strong as ever.
In fact, on a desirability scale, women's yearnings decreased steadily with every passing month of a relationship, making it possible to gauge a woman's sex drive just by looking at a union's duration, the Daily Mail reported.
For the study, desire levels of170 men and women were monitored and rated on the Female Sexual Function Index.
Participants, all in heterosexual relationships ranging from one month to nine years in length, were all undergraduates at the University of Guelph in Ontario, Canada, where the study's lead researcher, Sarah Murray, is based.
Ranging from 1.2 to 6.0, the scale quantifies sex drive so accurately that Murray and her research partner Robin Milhausen found "specifically, for each additional month women in this study were in a relationship with their partner, their sexual desire decreased by 0.02 on the Female Sexual Function Index".
According to Live Science, the findings lead the researchers to believe that relationship duration is a better predictor of sexual desire than satisfaction in bed or overall relationship health.
The study contradicts some beliefs that both men's and women's sex drives decline over the months and years.
Instead, a sustained desire by men is thought to be driven by the evolutionary need for men to produce offspring while women turn their focus to child-rearing, the science site stated.
While hormone levels may play a role in both men's and women's desirability levels, the researchers cautions over-exaggerating their importance rather than acknowledging the place of "satisfying, loving relationships" and having "time to feel relaxed, playful and sexy", according to the science site.
Murray concluded "when an individual has had sex with their partner over the course of many, many years, it takes creativity and openness to keep things fresh and exciting".
She says it is "crucial" to put effort into keeping things "fun and interesting"'' in the bedroom.
The study was published last month by the Journal of Sex and Marital Therapy