About 5% of pre-eclampsia cases during pregnancy could be tied to exposure to polluting ozone during the first trimester, new research suggests.
Pregnant women with asthma could be at a higher risk of the serious condition, the major study published in the online journal BMJ Open found.
Pre-eclampsia can lead to major complications if not treated. High blood pressure and protein in the mother's urine during the pregnancy are characteristic of pre-eclampsia.
The researchers studied data from 1998 to 2006 on 121,000 single baby births in Greater Stockholm, Sweden, as well as asthma statistics on the children's mothers and the amounts of ozone and vehicle emissions of nitrogen oxide - both air pollutants - in Stockholm.
The researchers said there is increasing evidence linking premature birth to air pollution. At the same time, asthmatics who are pregnant have a greater risk of suffering complications during pregnancy, including pre-eclampsia and low birthweight babies.
All told, there were 4.4% of premature births from the total pregnancies, while the rate of pre-eclampsia was 2.7%.
The study found no link between pregnancy complications and exposure to vehicle exhaust levels, nor did the researchers find links between underweight babies at birth and exposure to any air pollutants.
However, there were indicators that exposure to increased ozone levels during the first trimester of pregnancy was linked to a higher risk of premature birth - when the baby comes before 37 weeks - and pre-eclampsia. The study was adjusted to take into account factors that could affect the outcome as well as seasonal adjustments in air contaminants. Spatial variations in exposure were not adjusted.
The risks of premature birth and pre-eclampsia increased by 4% for every 10 ug/m3 increase in ambient ozone during the first trimester, the study results suggested. Asthmatics who were pregnant had a 25% greater chance of having a premature baby and a 10% greater chance of suffering pre-eclampsia, than mothers without asthma.
The study authors concluded that 5% of pre-eclampsia cases, or one in every 20 cases, were tied to the mother's exposure to ozone levels during the first three months of her pregnancy. They reached this calculation after factoring in the age of the pregnant woman, previous births, level of education, ethnic background, asthma, year and season of conception.
Copyright Press Association 2013