The horrific 9/11 terror attacks may have also led to increased loss of male children in the US, even among those women who had no direct link to the event.
Tim Bruckner, assistant professor of public health at the University of California Irvine and colleagues at UC-Berkeley found that the foetal death rate for males spiked in September 2001. Significantly fewer boys were born than expected in December 2001.
"The theory of 'communal bereavement' holds that societies may react adversely to unsettling national events, despite having no direct connection to persons involved in these events," Bruckner said.
"Our results appear to demonstrate this, as the shocks of 9/11 may have threatened the lives of male foetuses across the US." The findings were reported online in BMC Public Health.
Bruckner and his colleagues used foetal death data from all 50 states compiled by the National Vital Statistics System between January 1996 and December 2002 to calculate how many male foetal losses would be expected in a normal September.
Reviewing all foetal deaths occurring at or beyond the 20th week of gestation, they found male foetal losses rose three percent above expected levels in September 2001.
"Across many species, stressful times reportedly reduce the male birth rate," said Bruckner.
"This is commonly thought to reflect some mechanism conserved by natural selection to improve the mother's overall reproductive success."
The study found that the foetal death rate for males increased in October and November of that year.