Nationwide shock after the 9/11 terrorist attacks on New York may have led to an unexpected surge in miscarriages across the United States, say scientists.
Researchers found that numbers of lost male babies spiked around the time of the September 11, 2001 suicide attacks which destroyed the World Trade Centre.
Throughout the US, significantly fewer boys were born two months later than they should have been.
A review of all foetal deaths occurring at or after the 20th week of pregnancy showed that male losses rose 3pc above expected levels in September 2001.
Dr Tim Bruckner, assistant professor of public health at the University of California, Irvine, said: "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.
"Our results appear to demonstrate this, as the shocks of 9/11 may have threatened the lives of male foetuses across the US."
Almost 3,000 people lost their lives after Al-Qa'ida terrorists flew two hijacked passenger jets into the 110-storey World Trade Centre twin towers, causing both to collapse.
Dr Bruckner's team analysed foetal death rates from all 50 US states between January 1996 and December 2002 to calculate how many male losses would be expected in a normal September. The researchers focused on boys because, across many species, stress is known to reduce male birth rates.
A previous study had found male foetal death rates in California rose after the attacks.