The effect may be greater in mothers with asthma, the findings indicate.
The authors base their findings on almost 121,000 singleton births in Greater Stockholm, Sweden, between 1998 and 2006, national data on the prevalence of asthma among the children’s mothers, and levels of the air pollutants ozone and vehicle exhaust (nitrogen oxide) in the Stockholm area.
There’s a growing body of evidence that points to a link between air pollution and premature birth, say the authors, while pregnant women with asthma are significantly more likely to have pregnancy complications, including underweight babies and pre-eclampsia.
In all, 4.4% of the pregnancies resulted in a premature birth and the prevalence of pre-eclampsia was 2.7%. There was no association between exposure to levels of vehicle exhaust and complications of pregnancy, nor were any associations found for any air pollutants and babies that were underweight at birth.
But there did seem to be a link between exposure to ozone levels during the first three months of pregnancy and the risk of premature birth (before 37 weeks) and pre-eclampsia, after adjusting for factors likely to influence the results and seasonal variations in air pollutants, although not spatial variations in exposure.
Each rose by 4% for every 10 ug/m3 rise in ambient ozone during this period, the analysis indicated. Mothers with asthma were 25% more likely to have a child born prematurely and 10% more likely to have pre-eclampsia than mothers without this condition.
After taking account of the mother’s age, previous births, educational attainment, ethnicity, asthma, season and year of conception, the authors calculated that that 1 in every 20 (5%) cases of pre-eclampsia were linked to ozone levels during early pregnancy.
The study is published by David Olsson and Bertil Forsberg, Department of Public Health and Clinical Medicine, Environmental Medicine, and Ingrid Mogren, Department of Clinical Sciences, Obstetrics and Gynaecology, all at Umeå University.
Dr David Olsson, Department of Public Health and Clinical Medicine, Occupational and Environmental Medicine, Umea University, Umea, Sweden.
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