The authors of a new paper in BMC Public Health 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.
Scientists from the University of California, Irvine and Berkeley 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. "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," said Tim Bruckner from the University of California at Irvine.
"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."
Citation: Tim A Bruckner, Ralph Catalano and Jennifer Ahern 'Male fetal loss in the U.S. following the terrorist attacks of September 11, 2001', BMC Public Health (in press)