October 15, 2013

Expert reaction to air pollution and low birthweight

The Lancet Respiratory Medicine published a study which found a significant association between exposure to common air pollutants during pregnancy and the risk of restricted fetal growth.

Dr Jenny Myers, NIHR Clinician Scientist/Clinical Senior Lecturer, Maternal & Fetal Health Research Centre, University Of Manchester, said:

“This paper uses measures of air pollutants and examines the relationship with low birthweight at term (some of the air pollutant measurements were available only at specific time points and therefore their level at the time of the pregnancies was estimated/extrapolated from these measurements). All preterm (<37 week) deliveries were excluded. The size of the effect of air pollutants on birthweight was smaller than the effect associated with maternal smoking, so for individual women smoking has the largest effect on low birthweight. For the whole population, however, air pollution has a greater effect because more women are exposed to air pollution than do smoke.

“Strengths of the study include its size and geographical spread. The effects of air pollutants in this study were also corrected for other confounders including maternal characteristics, education and smoking. Following adjustment the effect remained which adds important significance to the findings.

“There are several limitations associated with the measures of pollution. Data was not available on all measures for several of the cohorts and in some instances measures of air pollution were taken over a different time period to the birth cohort dates. It is important to note for UK readers that only traffic density data was included for the UK cohort as air pollutant data was not available.

“The mechanism by which air pollutants cause growth restriction is unknown, but it is plausible that environmental toxins could have a toxic effect on placental growth and function. This study has demonstrated a convincing association between air pollutants and low birthweight at term, evidence of causation, however, is not proven by this study.”

Professor Jean Golding, Emeritus Professor of Paediatric and Perinatal Epidemiology, University of Bristol, said:

“This is an interesting and important study which looks at the estimated particulate pollutant level outside the home based on the known industrial pollution and the types of traffic on the nearest road(s). It is important to note that the babies of women who smoked were most susceptible to the growth retarding effect. The association is suggestive, but we cannot assume that it indicates causality. If it were causal, the implications would be for manufacturers to develop diesel motors that had much reduced particulate pollution levels, and for purchasers to demand such products. After all if fetuses are being affected in this way how much damage is being done to the growth and development of young children?”

‘Ambient air pollution and low birthweight: a European cohort study (ESCAPE)’ by Marie Pedersen et al. published in the Lancet Respiratory Medicine on Tuesday 15 October 2013.