In the summer, the long days and intense heat can lead to romance blossoming.

And now experts believe it may be the best time of year to conceive a baby.

Researchers have discovered that sperm is more active during the summer months.

They believe that the months of July and August may be the best time to try for a baby, as sperm motility is considerably greater then, when compared to January.  

This could be due to changes in levels of hormones such as testosterone, the researchers suggest.

One in six couples now face infertility, which is defined as being unable to conceive after a year of trying for a baby.

Male infertility is responsible for around half of cases, with low sperm motility a contributing factor.

To fertilise an egg to make a baby, sperm must swim though a cervix, uterus and fallopian tubes and it's ability to do so quickly is known as motility.

Decreased sperm mobility will make it harder for your sperm to swim to the egg, and make conception less likely.

Men are most likely to be fertile when at least 40 per cent of sperm are moving.

As part of the study, doctors collected data from 5,188 men at the Centre for Reproductive Incapacity of the University Hospital of Parma, in northern Italy.

They found sperm motility peaked in the summer and was lowest in winter, even though the volume of sperm was highest in winter.

The number of men with sperm motility greater than 40 per cent, was 65.3 per cent in summer, dropping to 50 per cent in winter.

This could be due to seasonal changes in hormone levels, the researchers said.

'We have shown the existence of a seasonal variation in some functional aspects of human semen,' said Dr Alfredo De Giorgi, writing in the study.

The research was published in the journal Chronobiology International.