The stress caused by psychological shock from the 9/11 terrorist attacks, felt even by people with no direct link to the event, may have led to an increased number of male children being miscarried in the US, say researchers writing in the open access journal BMC Public Health who claim to have found that the fetal death rate for boys spiked in September 2001, and that significantly fewer boys than expected were born in December of that year.

Tim Bruckner from the University of California at Irvine worked with researchers from the University of California at Berkeley to carry out the study. He 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 fetuses across the U.S."

Bruckner and his colleagues used data from the National Vital Statistics System, which compiles fetal death data from all fifty states of the US, from January 1996 to December 2002 to calculate how many male fetal losses would be expected in a 'normal' September.

They found that in September 2001, this figure was significantly exceeded. Speaking about the reasons for this, Bruckner said, "Across many species, stressful times reportedly reduce the male birth rate. This is commonly thought to reflect some mechanism conserved by natural selection to improve the mother's overall reproductive success." Source: BioMed Central