Pregnant women and their offspring: a high-risk group for air pollution

According to a British study, infant mortality rises when pregnant women are exposed to air pollution during pregnancy [1]. Air pollution during pregnancy can have long-term impacts and affects lung function even in school children [2].

Pregnant women and their offspring are uniquely susceptible to adverse effects of air pollution exposure [3]. Previous studies have shown that exposure to air pollutants during pregnancy – even in small concentrations — can lead to adverse birth outcomes, such as low birth weight, which might impact mortality [4,5]. This was confirmed by research presented during the ERS congress [1,2]. Data of nearly 8 million live births between 2001 and 2012 in England and Wales were analysed by Dr Sarah Kotecha (Cardiff University School of Medicine, United Kingdom) and her colleagues [1].

The aim of the study was to investigate whether exposure to nitrogen dioxide (NO₂), sulphur dioxide (SO₂), and particulate matter with an aerodynamic diameter ≤10µm (PM₁₀) is linked to all-cause infant, neonatal, and post-neonatal mortality. For their analysis, they divided the territory into approximately 35,000 areas with about 1,500 residents each. Ranking scores were calculated by quintiles for each pollutant and each year; thereafter, the lowest quintile was defined as a reference.

The researchers were able to determine that the highest pollutant exposure was associated with a 24-43% higher mortality risk for infants, 21-38% higher risk for neonates, and 32-54% for post-neonates, compared with infants living in the least polluted areas [1]. Subsequently, the researchers adjusted for deprivation, birth weight, maternal age, sex, and multiple births, which were all identified as possible confounders. In the end, the odds ratios (OR) for infant deaths sank but remained significantly raised for NO₂, SO₂, and PM₁₀ to 1.07, 1.19, and 1.04, respectively.

Interestingly, some of the pollutants showed different levels of influence at different ages. All pollutants had a significant association with augmented post-neonatal mortality, but only SO₂ lead to a significantly higher risk of neonatal death (OR 1.21). According to Dr Kotecha, these different associations of SO₂ and the other pollutants might be a result of different biological mechanisms. “Our findings show that although progress has been made, the challenge remains to reduce air pollution in order to reduce the numbers of infant deaths. In the meantime, by understanding how pollution affects babies, either directly or via the mother, we may be able to develop appropriate therapies or other interventions, depending on the amount of exposure to the different types of pollutants,” said Dr Kotecha [1].

Exposure early in pregnancy associated with lower lung function in school children

Exposure to air pollution from road traffic in the first trimester of pregnancy and in early life can even affect lung function of 8-year-old children [2]. This was shown by the Avon Longitudinal Study of Parents and Children (ALSPAC), the largest study to date to investigate the impact of particulate matter (PM₁₀) from different sources, including road traffic, on lung development and growth.

In this study, exposure to PM₁₀ between 1990 and 2008 in 13,963 children was calculated for each trimester of pregnancy, and at the ages of 0-6 months, 7-12 months, and then annually to the age of 15 years. In addition, lung function tests, the Forced Expiratory Volume in 1 second (FEV1) and Forced Vital Capacity (FVC) test were performed in children at the age of 8 and 15 years. The results were adjusted for age, gender, and height.

Exposure of children to PM₁₀ from traffic varied from 0 to 8 µg/m³ over the periods measured. Every 1 µg/m³ increase above zero during the first trimester was associated with a 0.8% reduction in lung function. This corresponded with an average reduction in FEV1 and FVC of 14 and 16 mL, respectively, by the age of 8 years [2]. Similar associations for exposure to traffic PM₁₀ during the second and third trimesters, over the whole pregnancy, and up to the age of 8 were found in the study. “Exposure to road traffic PM₁₀ in very early life showed harmful associations with lung function in 8-year-olds,” said Prof. Anna Hansell (University of Leicester, United Kingdom) during the presentation of the study. “Associations were stronger among boys, and children whose mother had a lower education level or smoked during pregnancy.”

Therefore, air pollution in pregnancy and early life may affect children’s development and potentially their long-term health trajectory. Interestingly, no associations between traffic pollution and lung function were noticed in children at the age of 15 years. One hypothesis by Prof. Hansell is that the effect of air pollution is relatively small and lung growth is able to outpace the adverse effects in teenagers. Another reason might be that air pollution levels, particularly diesel emissions, were reduced over time.

The mechanisms behind the harmful effect of PM₁₀ during pregnancy are still a matter of debate. Particles may cross the placenta and disturb the development of the growing foetus’s lungs through oxidative stress.

1. 
   
   1. Kotecha S, et al. Poster PA1027, ERS 2019, 29 Sept-2 Oct, Madrid, Spain.
   2. Hansell A, et al. Abstract No. OA482, ERS 2019, 29 Sept-2 Oct, Madrid, Spain.

 



Posted on 28 November 201917 March 2021