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Invisible 9/11 victims: the unborn
Sept. 1, 2006
Special to World Science
The horrors of Sept. 11,
2001 apparently triggered miscarriages of hundreds of unborn boys in New York City, and even more across the United States, researchers say. Send us a comment
on this story, or send
it to a friend
The findings
are drawing attention to a phenomenon that scientists
are only beginning to understand: the number of
boys born in disaster-struck areas typically drops as a percentage of total births.
Researchers speculate that this might be because a mother’s stress can kill
some fetuses, and that males especially are at risk.
The new findings
suggest such a drop occurred
dramatically in New York after the Twin Towers tragedy: the
count of boys born compared to girls plunged from roughly normal rates to
ones unseen nationally since 1940, when the record-keeping began.
Scientists at the University of California, Berkeley examined statistics for January, 2002, four months after the attacks. They
found a five-point drop in the percentage of male births compared to
average.
This helped make that whole year the poorest for newborn boys of any between 1996 and 2004, the latest for which figures are available,
as city Health Department statistics indicate. These same figures show 999 fewer boys born in that year compared to the average of the other years. There is also an
analogous but smaller dip in newborn girls, of 593.
The Berkeley study found that in January of that year, just about the same number of boys and girls were
born—an anomaly. Normally there are about 105 male births per 100 female
births. A crash in boy births of this magnitude would correspond to
well over 200 “missing” babies for January alone.
The problem wasn’t limited to New York, the Berkeley
researchers said. Previous research by them showed a smaller but still noticeable dip in male birthrates in far-off California, the December after the disaster. There, the number fell to under 103 male births per 100 female.
Nationwide, federal statistics put male birthrates for the year of the attacks at a record low, barely. But it’s unknown whether the attacks were a
significant factor in
that. This would leave unexplained why in New York, the major recorded decrease didn’t occur until
the next year.
The national statistics, from the Centers for Disease Control, show 104.6 newborn boys per 100 newborn girls the year of the disaster,
a record low since the government started keeping track in 1940.
The second lowest year, one decade earlier, was just a hair higher and
rounds off to the same number. Whatever its cause, the low point meant almost 11,000 boys less than
an average year.
One explanation for post-trauma shortages of male babies might
be that a spike in a mother’s stress hormones “increases the risk of death among weaker males,” wrote the Berkeley researchers in the May 2005 issue of the research journal
Human Reproduction.
Some scientists speculate that “these hormones perturb males in gestation more than females,” they added in the paper, which described the California study. Their more recent New York study appears in the journal’s Aug. 26 advance online edition.
Higher male vulnerability in the womb would mirror the fact that boys are weaker than girls as infants.
The latter explains why boys and girls are typically about equal in number by age 5, even though more boys are
born: males suffer higher infant mortality.
Scientists have debated why disasters lead to a drop in the percentage of male births, said the Berkeley researchers, led by Ralph Catalano. One theory holds that such events somehow increase the likelihood of girls being conceived. But the
birthrate changes following Sept. 11 occurred much too early to be explained by that, Catalano argued.
That would leave the other possibility, that stress killed some fetuses.
Strangely, although sudden disasters such as earthquakes seem to
produce such effects consistently, prolonged hardships
such as wars and poverty don’t,
the researchers noted—so the role of stress, if any, is not
simple.
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The 2001 World Trade Center attacks apparently triggered miscarriages of hundreds of unborn boys in New York City, and even more across the United States, researchers say. Past studies have noted that the number of baby boys born in areas struck by natural disasters typically drops as a percentage of total births. Scientists speculated that this might be because a mother’s stress can somehow kill weaker fetuses, and that males are especially vulnerable. New research has found that the effect appeared dramatically in New York after the Twin Towers tragedy: the number of newborn boys compared to girls plunged from roughly normal rates to levels lower than any seen nationally since 1940, when authorities started keeping records. Scientists at the University of California at Berkeley examined birthrate statistics for January, 2002, four months after the attacks. The dip in male births contributed to making that year the poorest for newborn boys of any year between 1996 and 2004, the latest for which figures are available, as documented in city health department statistics. These same figures show 999 fewer boys born in that year compared to the average of the other years. There is also a corresponding but smaller drop in newborn girls, of 593. The study found that in January of that year, just about the same number of boys and girls were born, a dramatic anomaly. Normally there are about 105 male births per 100 female births, both in New York and nationwide, consistent with global averages. The crash in boy births the researchers recorded would correspond to more than 200 “missing” babies for January alone. The problem wasn’t limited to New York, the Berkeley group argued. Previous research by the same team showed a smaller but still noticeable dip in male birthrates in far-off California, the December after the disaster. There, the number fell to under 103 male births per 100 female. Nationwide, federal statistics show that male birthrates for the year of the attacks at a record low, barely. But it’s unknown whether the attacks were a significant factor in that: this would leave unexplained why in New York, the major recorded decrease didn’t occur until the following year. The national statistics, from the Centers for Disease Control, show 104.6 newborn boys per 100 newborn girls the year of the disaster, the lowest since the government started keeping track in 1940. The previous record, a decade before the tragedy, was barely a hair higher and rounds off to the same number. One explanation for the shortages of male babies is that a spike in a mother’s stress hormones “increases the risk of death among weaker males,” wrote the Berkeley researchers in the May 2005 issue of the research journal Human Reproduction. Some scientists speculate that “these hormones perturb males in gestation more than females,” they added in the paper, which described the California study. Their more recent New York study appears in the journal’s Aug. 26 advance online edition. Increased male vulnerability in the womb would mirror the well-known fact that boys are weaker than girls as infants. That fact explains why males suffer higher infant mortality, and thus why boys and girls are typically about equal in number by age 5, even though more boys are born. Scientists have debated why disasters lead to a drop in the percentage of male births, said the Berkeley researchers, led by Ralph Catalano. One theory holds that such events somehow increase the likelihood of girls being conceived. But the decreases that his group identified occurred much too early to be explained by that, Catalano argued—leaving the other possibility, that stress killed some fetuses.