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Friday 20th April 2018

Fewer boys after 9/11

9th September 2006

23052006_groundzero1.jpgResearch reported in the BMJ suggests that anxiety and stress in New York city in the aftermath of the terrorist attack on the World Trade Center five years ago may have resulted in the birth of fewer boys months later.

The study, based on more than 700,000 births in New York city between January 1996 and June 2002, shows that the birth sex ratio for the city dropped to below one in the January after the attacks, its lowest level. 

Previous research has indicated the sex ratio falls in populations subjected to external stressors, with the odds of a male birth falling with earthquakes, political and social upheavals, and economic downturns. One theory is that, particularly in women in the second and early third trimesters of their pregnancy, the stress of the attack resulted in a disproportionate loss of male foetuses, lowering the odds of a male birth. Another explanation is that stress may reduce the conception of boys.

The authors, from the school of public health at the University of California in Berkeley, say that their findings support the male foetal loss explanation; as the sex ratios eight, nine, and 10 months after the attacks did not fall, the reduced conception theory seems unlikely.

The researchers say that it is not clear why cohorts in the 20th-24th weeks of pregnancy seemed to be the most vulnerable. "The answer may be related to the finding that the foetal response to maternal stressors appears strongest in the second half of gestation and that mothers may use that response as a test of male fetal robustness," they say.


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