Stress caused by psychological shock from the Sept. 11, 2001 terrorist attacks, felt even by people with no direct link to the event, may have led to an increase in male children being miscarried in the U.S.
Tim Bruckner, assistant professor of public health at UC Irvine, and colleagues at UC Berkeley found that the fetal death rate for males spiked in September 2001 and that significantly fewer boys were born than expected in December of that year. They report their findings online in the open access journal BMC Public Health
"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 fetuses across the U.S."
Bruckner and his colleagues used fetal death data from all 50 states compiled by the National Vital Statistics System between January 1996 and December 2002 to calculate how many male fetal losses would be expected in a normal September. Reviewing all fetal deaths occurring at or beyond the 20th week of gestation, they found male fetal losses rose 3 percent above expected levels in September 2001.
"Across many species, stressful times reportedly reduce the male birth rate," said Bruckner, in explaining this phenomenon. "This is commonly thought to reflect some mechanism conserved by natural selection to improve the mother's overall reproductive success."
Ralph Catalano and Jennifer Ahern of UC Berkeley contributed to the study, which expands upon a 2005 study in which Berkeley researchers examined fetal death and birth-sex ratios in California following the Sept. 11 terrorist attacks. They found that the fetal death rate for males increased in October and November of that year.