More babies are born in September than any other time of year, and it's all to do with something that happens around Christmas (and very little to do with how much sex you're having).
For those planning to start or expand their family, finding out how to increase fertility and keeping track of an ovulation calculator is common practice. However, research suggests a bit of cold weather might be all that some couples need in order to increase their chances of getting pregnant. So put away your list of Christmas baby names, because the late summer baby boom is a very real thing.
The phenomenon occurs because more babies are conceived over the festive period than any other time of year, but while many people think cosy season equals more time for having sex, it turns out there's a much more scientific reason why so many people get pregnant during the holidays.
A study in the Obstetrics & Gynecology journal found that men with normal sperm production had the healthiest sperm in winter and early spring, producing 70 million sperm per millilitre of semen compared to 68 million at the end of spring.
In addition, sperm produced in the winter were faster than their spring counterparts - making them more likely to reach an egg and improving the chances of conception. Essentially, this means that sperm quality improves in the winter compared to warmer months.
But it's not just sperm that changes with the seasons. The researchers also found that the ovum - a mature female reproductive cell - becomes more receptive to sperm in the winter.
This results in more babies being born in September and October than any other time of year, with data from the Office for National Statistics (ONS) showing that the most popular day of the year to be born is September 26. This suggests that the most popular time to conceive is two days after Christmas, on December 27.
Meanwhile, eight of the top 10 dates of birth were towards the end of September - with the other two being in early October.
However, the ONS suggests another reason for the September baby boom, saying, "Part of the reason for this increase in births could be due to couples planning to have children at the start of the school year."
And, it's true, that the birth month of young children can affect their educational attainment, with research published by the Institute of Fiscal Studies (IFS) suggesting that children born during autumn months - the beginning of the academic year - were on average achieving better exam results.
For more on conception and fertility, we've taken a look at how to increase sperm count and the possible reasons why you can't get pregnant. Find out what is ovulation exactly too.
