The California Birth Defects Monitoring Program is
capable of springing into action when there is concern
that local environmental conditions may be linked
to birth defects. Small area investigations can be
reactive or proactive, responding to community cluster
reports or an environmental emergency.
INVESTIGATING BIRTH DEFECTS CLUSTERS
A cluster is a mini-epidemic, where too many affected
babies are born in a short time span. Birth defects,
like other health conditions, often occur in clusters.
Most happen by coincidence or chance alone. Others
can be explained by changes in medical practices.
Very rarely, a cluster is due to a teratogen—an
environmental exposure that causes birth defects.
IN THE AFTERMATH OF AN ENVIRONMENTAL CRISIS
Occasionally, an environmental emergency prompts
concerns. For example, in 1991, The Program tracked
over 100 pregnancies conceived shortly before or
after a massive spill of the toxic herbicide metam-sodium
into the Sacramento River. (We determined that birth
defects were not elevated.)
HALLMARKS OF A TERATOGEN
A local investigation can only detect “sledgehammers”--very
potent teratogens. Otherwise, the limited numbers
involved aren’t statistically powerful enough
to resolve questions. At best, small area studies
generate clues—even if results are suspicious,
they must be confirmed with a larger case-control
study.
In evaluating community concerns, we look for the
features noted in scenarios where teratogens have
been involved:
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cases
with the same or developmentally related
birth defects |
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a large increase (more than
10 times the expected rate) |
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an exposure in common.
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 Investigating
Birth Defects Clusters: A Systematic Approach |
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REFINEMENTS OVER TIME
When the Program began, we hoped that cluster investigations would
generate clues about birth defects causes. But after investigating
more than 200 clusters—which raised anxiety but rarely provided
answers—we identified no teratogens. We re-examined our strategy
and found:
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Random fluctuation probably accounts
for most rate variation in small populations. |
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Small numbers have no statistical power. Even if
a teratogen is present, it would have to increase risks dramatically
to be detected. |
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Research studies are the best way to identify causes.
When there is an environmental concern—such as pesticides—large-scale,
rigorous studies are more informative than drawing conclusions
from a small area. Research can identify the “sledgehammers” and
pinpoint subtle risk factors. |
RAPID RESPONSE CAPABILITY
It is still important to have a crisis response plan. When action is
warranted, the California Birth Defects Monitoring Program can quickly
mobilize data collection specialists and a scientific team to collect
and evaluate data and respond to public concerns.
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SMALL AREA INVESTIGATIONS
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