Trying to get pregnant? These are the exact times in the year men are most fertile.

Image via 20th Century Fox.

The cast of Grease may have been onto something – a new study suggests that summer lovin’ could be the key to conceiving, finding that sperm is more active in the main months of summer (so January and February in Australia, July and August for the northern hemisphere) and twice as active in this period compared to winter.

Doctors analysed data collection from over 5,000 men attending Northern Italy’s Centre for Reproductive Incapacity (a service offered by University Hospital of Parma), aiming to assess the presence of a possible seasonal pattern in sperm quality.

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Researchers largely looked at sperm motility, which refers to the way the sperm moves and it’s ability to swim. This movement is essential in enabling the sperm to swim through a female’s cervix, uterus and fallopian tubes to reach and fertilise an egg.

They found that compared with other seasons of the year, a higher sperm motility was found during the summer. Spring was found to be the time with the highest prevalence of samples with a normal sperm pH (7.2-8), whilst the volume of sperm was higher in winter. (Post continues after gallery.)

Poor sperm motility is also one of the main factors in male infertility, which is responsible for about half the cases of infertility. Infertility is defined as the “inability to conceive after 12 months of trying” and is said to affect around 15  per cent of Australian couples.

“We have shown the existence of a seasonal variation in some functional aspects of human semen,” said Dr Alfredo De Giorgi who led the study, published in the journal Chronobiology International.

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It is believed that seasonal changes in levels of hormones including testosterone may be responsible.

The Independent reports that for seasonal breeders (animals that successfully mate only during certain times of the year), light plays an important role in regulating reproduction to ensure that birth occurs at the most favourable time of the year.

These latest results build on previous studies but the results are conflicting with existing research which found heat has a negative effect on sperm.

A 2013 Israeli study (among others) found sperm had greater numbers with faster swimming speeds and fewer abnormalities in semen made during winter, with a steady decline in quality from spring onwards. (Post continues after video.)

Published in the American Journal of Obstetrics and Gynecology, the head of the research team Dr Eliahu Levitas wrote that despite the evidence in animals, it remained unclear whether human sperm is also healthiest during certain times of the year.

The Israeli team did conclude however that knowledge of a seasonal pattern “may be of paramount importance, especially in couples with male-related infertility struggling with unsuccessful and prolonged fertility treatments.”

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So what should we believe?

Dr Dasha Fielder, principal doctor of Sapphire Family Medical Practise in Bondi says that the season shouldn’t be the main concern when it comes to fertility.

“Generally sperm survives better in colder environments and there are some studies that show sperm is healthier in winter, however I don’t think it is a significant variation and certainly not in Australian climate,” she says.

"What matters for sperm quality is whether or not a man has had injury to their testicles, has had infection such as mumps, if they are generally healthy, especially smoking or alcohol consumption."

For women, the main factors that affect is fertility are age (from the age of 30 fertility declines), STD's in the past and endometriosis or PCOS, Dr Fielder says.

Related: "I created vagina art for my husband and ended up in hospital."

A recent study also found that birth month could affect the number of diseases you're likely to get. How does your birthday stack up?

Do you think season affects fertility?