A British mathematician has revealed a surprising sex ‘hack’ that could make women who get pregnant more likely to give birth to a boy.
Professor Hannah Fry took to Instagram to discuss a peculiar trend, which involves a spike in baby boys being born after world wars have ended, known as the ‘the returning soldier effect’.
Pointing to graph showing the ratio of baby boys and girls born in England and Wales she explained: ‘You’ve got some really definite peaks — one in 1919 just after the end of the First World War, another one in 1945 just after the end of the Second World War‘.
The academic and television presenter said evidence suggested this phenomenon was the result of a combination of social circumstances and a quirk that makes women more likely to have boy if conception occurs early in their ‘fertile window’.
Professor Fry said people tend to have more sex after wars as soldiers come home to their wives or lovers, leading to greater chances of conception.
This increased frequency of sex means a woman is more likely to become pregnant earlier in her cycle, and Professor Fry highlighted it was this aspect that could lead to a peak in baby boys.
‘The chances of a woman conceiving a male or female child actually very subtly changes depending on when in her cycle she conceives,’ she said.
‘So slightly earlier, ever so slightly more likely that she’ll have a baby boy.’
This Government graph shows the ratio of male births (purple line) compared to 100 female births in England and Wales, Scotland and Northern Ireland between 1910 and 2021
Experts have theorised that this may be due to differing hormonal or acidity levels within a woman’s cycle, which can alter the environment of the cervix.
These changes make it more likely sperm carrying a Y chromosome, which makes a boy, will successfully reach the egg first.
Other studies suggest an imbalance in boys and girls is due to a very slight increase in female embryo mortality compared to males.
But Professor Fry warned that those hoping to use the early cycle method to influence the sex of their baby aren’t guaranteed success.
She explained that on an individual level the increased chance of having a boy is ‘tiny’.
‘When you scale up to the size of a population this becomes a pattern that becomes really clear,’ she said.
The returning soldier effect, despite the name, isn’t always linked to conflict, Prof Fry said.
Another spike in baby boys was seen in Britain in 1973 when the country was experiencing an energy crisis, and many people were only working outside of the home a few a days a week.
But Professor Fry warned that those hoping to use this system to influence the sex of their baby would likely be unsuccessful. Stock image
‘I think we now know what everyone in Britain was doing during their three day week,’ Professor Fry said.
While the ‘the returning soldier effect’ is real, it’s worth highlighting that even in normal periods slightly more baby boys are born than girls.
This typically translates to roughly 104 boys for every 100 girls.
This doesn’t make a difference to the population as, statistically, slightly more boys die before reaching adulthood than girls, generally through accidents or developmental problems.
[Notigroup Newsroom in collaboration with other media outlets, with information from the following sources]
