The secondary sex ratio (i.e., the odds of a male birth) reportedly falls in populations subjected to natural disasters [1
], pollution events [2
], and the contraction or collapse of economies [3
]. Drops in the secondary sex ratio deserve public health attention because the literature indicates that male fetal loss may contribute to this decline [5
] Although the biological mechanism remains unclear, male fetuses appear more sensitive than female fetuses to maternal corticosteroids produced after the twentieth week of gestation [6
]. This elevated stress reactivity apparently jeopardizes the viability of males in utero
. Consistent with the theory of natural selection, humans may have conserved this male fetal sensitivity to maximize the mother's total yield of grandchildren [8
One study in California suggests male fetal loss may follow stressful events. The authors report that ambient economic decline precedes an increased risk of a male fetal death [9
]. Mechanisms other than male fetal loss, however, may account for the inverse association between environmental stressors and the secondary sex ratio. Ambient stressors may decrease the odds of a male conception by reducing sperm motility or the frequency of coitus [10
]. Fukuda and colleagues, for instance, found sub-optimal sperm motility among Japanese males after the Kobe earthquake [12
Distinguishing between the male fetal loss and reduced male conception explanations holds implications for public health. Whereas reduced male conceptions may interest basic researchers, fetal loss induces psychological, if not somatic, morbidity. Mothers who report a stillbirth or spontaneous abortion also exhibit an elevated incidence of subsequent adverse birth outcomes [13
]. For these reasons, fetal loss remains the object of much clinical intervention.
The terrorist attacks of September 11, 2001 induced widespread social and economic disruption, leading to high levels of stress and anxiety in the United States population [15
]. The attacks' discrete temporal nature allows us to test whether and when they increased male fetal loss. One report of the fetal death sex ratio (i.e., odds of a male fetal death) after September 11 appears in the literature. In California, the fetal death sex ratio increased one month after the attacks [18
]. Reports in California and New York City also indirectly support the male fetal loss explanation, as the secondary sex ratio decreased three and four, but not eight, nine, or ten, months after the attacks [19
These findings raise the obvious question of whether male fetal loss increased in the remainder of the United States (U.S.) following the terrorist attacks. This test could assist in understanding the extent to which pregnant mothers experienced "communal bereavement" after September 11. Although most research on bereavement concerns individuals with direct relationships to the deceased, work by Catalano and Hartig [20
] indicates perinatal sequelae among the broader society without such social ties. The authors posit that a nation's population of pregnant women may experience widespread distress even if they never met the deceased, particularly after events in which institutions such as the state fail to maintain safety and security for its members. We believe that the terrorist attacks of September 11, 2001 meet this condition. Much epidemiologic literature, moreover, reports a nationwide increases in acute mental distress following the attacks of which the overwhelming majority of respondents had no direct relationship to the deceased [15
]. We also know of no reports that pregnant women in particular sheltered themselves from this distress.
We test the communal bereavement hypothesis that the fetal death sex ratio in the U.S. (less California) rose above its expected level following September 11, 2001. Consistent with theory and earlier empirical research, we, as described below, focus our fetal loss test in September, October, and November 2001 [18
]. If results support male fetal loss, we then test the attending hypothesis that the secondary sex ratio in the U.S. (less California and New York City) will fall below its expected value two, three, or four months after September 11, 2001.