Abstract:
Background Individual studies on the relations
between ambient air pollution and the risk of stillbirth
have provided contradictory results. We conducted a
systematic review and meta-analysis to summarise the
existing evidence.
Methods We conducted a systematic search of three
databases: PubMed, Scopus and Web of Science, from
their time of inception to mid-April, 2015. Original
studies of any epidemiological design were included.
Data from eligible studies were extracted by two
investigators. To calculate the summary effect estimates
(EE), the random effects model was used with their
corresponding 95% CI.
Results 13 studies met the inclusion criteria. Although
not reaching statistical significance, all the summary
effect estimates for the risk of stillbirth were
systematically elevated in relation to mean prenatal
exposure to NO2 per 10 ppb (EE=1.066, 95% CI 0.965
to 1.178, n=3), CO per 0.4 ppm (EE=1.025, 95% CI
0.985 to 1.066, n=3), SO2 per 3 ppb (EE=1.022, 95%
CI 0.984 to 1.062, n=3,), PM2.5 per 4 μg/m3
(EE=1.021, 95% CI 0.996 to 1.046, n=2) and PM10 per
10 μg/m3 (EE=1.014, 95% CI 0.948 to 1.085, n=2).
The effect estimates for SO2, CO, PM10 and O3 were
highest for the third trimester exposure. Two time series
studies used a lag term of not more than 6 days
preceding stillbirth, and both found increased effect
estimates for some pollutants.
Conclusions The body of evidence suggests that
exposure to ambient air pollution increases the risk of
stillbirth. Further studies are needed to strengthen the
evidence.
