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Couples who have been together for a very long time often attribute their relationship success to a number of different things, from not going to bed on an argument to regularly enjoying dates.

However, they may be unaware that the likelihood of them staying together and going the distance could have been marked out the first time they had sex.

Researchers from the University of California have carried out a study involving more than 800 people and found that the success of a relationship may be defined by the chemistry that is sparked on that very early sexual adventure.

Perhaps unsurprisingly, those who enjoyed fireworks the first time were more likely to stick together and have the potential to turn that union into a long-term relationship than those whose love-making wasn't particularly memorable.

In the study, lead author Professor Paul Eastwick looked at relationships from beginning to end and used a pioneering technique that got those involved to recall experiences from throughout their past.

The scientists found that almost all relationships are identical in their earliest stages, which is when you're likely to get that head-over-heels, can't-keep-your-hands-off-them kind of feeling. This was an unreliable indicator of whether or not any given relationship would go the distance.

Eventually though, after weeks or months, the trajectories of successful versus unsuccessful unions started to pull apart. For short-term relationships, romantic interest plateaued and then took a nosedive, but it carried on climbing among couples who then had gone on to stay together.

And what was the key factor in determining whether people got married or broke up? Professor Eastwick said it was likely to be the point at which the couple became intimate.

"People would hook up with some partners for the first time and think 'wow, this is pretty good.' People tried to turn those experiences into long-term relationships. Others sparked more of a 'meh' reaction. Those were the short-term ones," the expert added.

Writing in the Journal of Experimental Psychology: General, Professor Eastwick explained that it puts a new perspective on the idea that exciting initial encounters are typically flings while long-term love can take time to develop as a slow burn.

According to a study published a few years ago to coincide with romantic novel The Rosie Project, women typically have seven relationships and seven sexual partners before meeting the person they'll settle down with. For men, the figures are eight and ten respectively.

What do you think? Were you able to tell from the first time you slept with someone that there was potential there, or do you think the researchers are reading too much into those early fumbles?