The Headline:
‘Mothers living near busy roads “have smaller babies,” The Times has reported. The newspaper said a new study found that exposure to traffic pollution could affect fetal development and lead to an increased chance of having a small baby.
NHS Choices says that:
The conclusions of the researchers seem valid and the size of this study adds to the confidence in the suggestion that air pollution, perhaps from traffic emissions, during early and late pregnancy may affect fetal growth.
There are a few points to note about this study:
- It is not clear exactly how air pollution might act to restrict fetal growth and it is possible that other aspects of the women’s lives may have influenced the chance of having a small baby.
- It is plausible, as the researchers say, that air pollution might alter cell activity or cut the amount of oxygen and nutrients a baby receives while in the womb but this will need separate evaluation.
- Studies looking at outcomes where multiple risk factors can affect the outcome are particularly prone to confounding. The researchers have tried hard to take these into account by adjusting for smoking and social-economic background. However, other factors that are linked to small babies, such as diet or maternal height could still be having an effect.
- Only 25% of births had both data on all the risk factors of interest and a residence less than 10km from a monitoring station, making this an urban study. This may limit the application of the results to more suburban or rural areas.
- Ideally, an ultrasound confirmed gestational age would have added reliability to the estimate of duration of pregnancy. Babies can also be small if they are born early.
While this is an important study into the effects of pollution on the chance of having a small baby, there are many additional socioeconomic and obstetric risk factors to take into account when putting this risk into context.
Links to the Headlines:
Pollution blamed for reducing birth weights. The Independent, April 09 2009
Pollution link with birth weight. BBC online, April 09 2009
Mothers living near busy roads ‘have smaller babies’. The Times, April 09 2009
Traffic pollution can harm babies in the womb, claim researchers. The Daily Telegraph, April 09 2009
Links to the Science:
Smedts HPM, de Rich DQ, Demissie K, Lu S-E et al.
Ambient air pollutant concentrations during pregnancy and the risk of fetal growth restriction. J Epidemiol Community Health. Published Online First: 8 April 2009
