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Abstract
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Background
The association between parental exposure to Agent Orange
or dioxin and birth defects is controversial, due to inconsistent
findings in the literature. The principal aim of this study was
to conduct a meta-analysis of relevant epidemiological studies
that examined this association and to assess the heterogeneity
among studies.
Methods
Relevant studies were identified through a computerized literature
search of Medline and Embase from 1966 to 2002; reviewing the
reference list of retrieved articles and conference proceedings;
and contacting researchers for unpublished studies. A specified
protocol was followed to extract data on study details and outcomes.
Both fixed-effects and random-effects models were used to synthesize
the results of individual studies. The Cochrane Q test and index
of heterogeneity (I2) were used to evaluate heterogeneity, and
a funnel plot and Egger's test were used to evaluate publication
bias.
Results
In total, 22 studies including 13 Vietnamese and nine non-Vietnamese
studies were identified. The summary relative risk (RR) of birth
defects associated with exposure to Agent Orange was 1.95 [95%
confidence interval (95% CI) 1.59-2.39], with substantial heterogeneity
across studies. Vietnamese studies showed a higher summary RR
(RR = 3.00; 95% CI 2.19-4.12) than non-Vietnamese studies (RR
= 1.29; 95% CI 1.04-1.59). Sub-group analyses found that the magnitude
of association tended to increase with greater degrees of exposure
to Agent Orange, rated on intensity and duration of exposure and
dioxin concentrations measured in affected populations.
Conclusion
Parental exposure to Agent Orange appears to be associated with
an increased risk of birth defects.
Keywords:
Agent Orange; dioxin; birth defects; meta-analysis; Vietnam.
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