Research Activities, October 2013
Male fetuses that survived the tragedy of 9/11 tended to be hardier at 2 years of age
After the terrorist attacks on September 11, 2001, there were reports of excess male fetal deaths in the following months. Natural selection theory supports that males in utero are more sensitive to outside stressors than females. However, a new study of births after 9/11 suggests that male fetuses that did survive the stress of 9/11 were hardier at 2 years.
The researchers collected data on cognitive scores and height for age on males born after 9/11 in California from the Early Child Longitudinal Study Birth Cohort. Excess male fetal loss took place in October and November 2001. By December 2001, there were 2 percent fewer live male births than expected. There were a total of 1,100 children at the 9-month assessment and 900 children at the 24-month assessment. The California group was then compared to children born in all other states.
Males born in December 2001 were found to have greater than expected cognitive function at 2 years of age. However, there was no consistent change in expected values in height-for-age. These California males with higher cognitive ability also had a lower incidence of very low birth weight, but this factor alone did not account for males' higher cognitive ability. The researchers also found that low socioeconomic status, a low score on the child's home environment, and birth weight were independent predictors of lower cognitive scores at 2 years of age.
Given the findings, the researchers conclude that after 9/11, more frail male fetuses may have been lost in utero compared to female fetuses. As a result, those males that did survive the stressors of the tragedy were hardier and had higher cognitive ability after 24 months. The study was supported in part by AHRQ (T32-HS00086).
See "Intrauterine stress and male cohort quality: The case of September 11, 2001," by Tim A. Bruckner, Ph.D., and Jenna Nobles, Ph.D., in Social Science & Medicine 76, pp. 107-114, 2013.