London, Nov 20 (IANS): Long-term relationships may offer many psychological benefits but staying in a monogamous relationship for long may reduce a woman's sexual desire, a study says.

Following over 2,000 premenopausal Finnish women for seven years, the researchers found that those who had stayed in the same monogamous relationship during the study period experienced the highest decrease in sexual drive.

The decrease in sexual desire was lower for women who had found a new partner over the study duration, said the study published in the journal Psychological Medicine.

"Our results advocate tailored psychobehavioural treatment interventions for female sexual dysfunctions that take partner-specific factors into account," said the study led by Annika Gunst from University of Turku in Finland.

The scientists used the Female Sexual Function Index -- a short questionnaire that measures specific areas of sexual functioning in women, such as sexual arousal, orgasm, sexual satisfaction, and the presence of pain during intercourse -- to look at the evolution of female sexual desire over a period of seven years, Medicalnewstoday.com reported.

Analyses were conducted separately for women in different relationship constellations.

Of the functions examined, the researchers found that women's ability to orgasm remained the most stable over the seven-year period, while sexual satisfaction varied widely.

During the seven-year follow-up, the ability to have an orgasm improved across all groups, with single women experiencing the greatest improvement.

Women with a new partner experienced higher improvement in orgasmic ability when compared to women who had been in the same relationship over the entire period of observation.