Improving Air Quality and Maternal Education Could Help Prevent Thousands of Cases of Low Birth Weight

Low birth weight can have profound and lasting consequences for health and development, from childhood through to adulthood. A study led by the Barcelona Institute for Global Health (ISGlobal), a centre supported by the ”la Caixa” Foundation, has examined the relationship between air pollution, maternal educational attainment and low birth weight in Spain. The findings, published in International Journal of Epidemiology, suggest that expanding access to higher education and reducing exposure to air pollution could significantly reduce cases of low birth weight.

The study analysed data from 1,409,084 births at term —defined as births occurring between 37 and 40 weeks of gestation— in Spain recorded by the Spanish National Statistics Institute (INE) between 2010 and 2018 and estimated exposure during pregnancy to nitrogen dioxide (NO₂) and fine particulate matter (PM₂.₅). The levels of these pollutants were calculated using models that combined pollution monitoring data with satellite information, meteorological data and characteristics of the surrounding environment. 

Low birth weight was defined as a birth weight below 2,500 grams. Among all the births analysed, 4.6% involved low birth weight. The percentage was higher among babies born to mothers with primary education (5.3%) than among those whose mothers had secondary (4.9%) or tertiary education (4.3%).

Higher risk associated with pollution and lower educational attainment

The results show an association between greater exposure to PM₂.₅ during pregnancy and an increased risk of low birth weight. Specifically, for every increase of 10 micrograms per cubic metre (µg/m³) in PM₂.₅ exposure, the odds of low birth weight increased by 6%. In the case of NO₂, an increase of 10 µg/m³ was associated with a 1% increase in the odds of low birth weight. The associations were more pronounced and precise among babies born to mothers with primary education, with 18.3% and 4.6% higher odds of low birth weight per 10 µg/m³ increase in PM2.5 and NO2, respectively, highlighting differences in vulnerability according to maternal educational attainment. 

Educational attainment showed a stronger association with the outcome. Compared with babies born to mothers with tertiary education, those whose mothers had secondary education had 32% higher odds of low birth weight, while among babies born to mothers with primary education, the odds were 76% higher.

“This greater vulnerability could reflect an accumulation of stressors, including nutritional deficiencies and more limited access to antenatal care, together with poorer maternal health and greater chronic stress, which could limit the ability to cope with the harmful effects of pollution,” says Stefan Sieber, ISGlobal researcher and first author of the study. 

Thousands of potentially preventable cases

The research team used statistical models to estimate how many cases of low birth weight could have been prevented under different hypothetical scenarios for reducing pollution. If exposure to PM₂.₅ had been limited during pregnancy to 10 µg/m³, the limit set by European legislation, there couldhave been 662 fewer cases between 2010 and 2018. With a limit of 5 µg/m³, corresponding to the World Health Organization (WHO) air quality guideline, the estimated reduction would have been 2,032 cases. For NO₂, limiting exposure to 20 µg/m³ (European legislation) was associated with an estimated reduction of 432 cases, while a limit of 10 µg/m³ (WHO guideline) was associated with an estimated reduction of 938 cases. 

The benefits of reducing pollution were clearer and greater among babies born to mothers with primary compared to higher education, consistent with the stronger association between pollution exposure and low birth weight in this group. In this group, for example, limiting PM₂.₅ concentrations to 5 µg/m³ would have reduced the estimated number of low birth weight cases from 8,349 to 7,974, a reduction of 759 cases (-9.1%), while in the secondary and tertiary groups the cases reduced by 2.2% and 2.6%, respectively. Limiting NO₂ to 10 µg/m³ would have resulted in an estimated reduction of 376 cases (-4.5%) in the primary group, while in the secondary and tertiary groups the cases reduced by 0.7% and 1.4%, respectively. These results highlight that air pollution reduction policies have the potential to reduce social health inequalities.

Increasing maternal education would have had a greater effect

The study also considered a hypothetical scenario in which all mothers had attained tertiary education, meaning advanced vocational training or a university degree. Under this scenario, the team estimated a reduction of 9,246 cases of low birth weight for PM₂.₅ and 9,275 cases for NO₂. The estimated prevalence of low birth weight would fall from 4.6% to 3.96%.

“Combining measures to reduce air pollution with social policies aimed at improving mothers’ educational attainment could significantly reduce the burden of low birth weight in Spain, particularly among the most vulnerable populations, helping to improve health equity,” says Cathryn Tonne, ISGlobal researcher and senior author of the study. 
 

Reference:

Sieber, S., Ballester, J., Nieuwenhuijsen, M., Pozzer, A., Tonne, C. The impact of improved air quality on low birth weight and health inequalities in Spain from 2010 to 2018. International Journal of Epidemiology, 2026. Doi: 10.1093/ije/dyag130