杏吧原创

There were fewer male babies born in England and Wales in mid 2020 than expected, possibly because the stress of the covid-19 pandemic led to more pregnancy losses of male fetuses.

Outside of the pandemic, more male babies tend to be born than female ones. Between 2012 and 2020, 1054 boys were born for every 1000 girls each year on average in England and Wales.

No one is sure why this happens. It may be because boys are more likely to die in infancy, so having more of them at the outset leads to聽a balanced sex ratio by the time babies reach reproductive age.

Several studies suggest there can be a sudden drop in the proportion of male births around three to five months after a stressful event that affects a whole population. This occurred , , and .

To find out if covid-19 had a similar effect, at Trinity College Dublin in Ireland and her colleagues analysed birth records spanning 2012 to 2020 for England and Wales.

In June 2020, the ratio of male to female babies born dipped suddenly, with only 1040 boys born for every 1000 girls. This was the lowest ratio of male to female babies of any June throughout the study period, with a statistical analysis suggesting this decline wasn鈥檛 a chance finding.

The drop in male births occurred three months after March 2020, when the first covid-19 deaths were reported in the UK, the country went into lockdown and the World Health Organization officially characterised the outbreak as a pandemic.

This suggests the initial stress of the pandemic caused a聽disproportionate loss of male fetuses among pregnant people in聽their second trimester, which may have resulted in fewer male babies being born in June 2020, according to the team.

Stressful events may activate non-conscious evolved mechanisms in pregnant people to聽spontaneously abort fetuses that have less chance of thriving in聽tough environments, says at the University of California, Irvine.

Male fetuses are more likely to be frail than female ones, meaning 鈥渢heir mothers may be unconsciously gauging that it鈥檚 not the best environment to bring them into鈥�, he says.

This may particularly occur during a pregnant person鈥檚 second trimester, assuming this is when they may unconsciously detect their fetus鈥檚 health, says Bruckner.

By August 2020, the ratio of聽male to female births had returned to pre-pandemic levels in聽England and Wales, possibly because people were habituated to聽the pandemic and the acute stress had passed, he says.

Since the drop in male births in聽England and Wales was small and short-lived, it won鈥檛 鈥渄istort the demographic characteristics in聽ways the average resident there聽would notice鈥�, says at the University of California, Berkeley.