(RxWiki News) Many cities and states announce Ozone Action Days when local ozone levels are high. Those may be good days for pregnant women to stay indoors.
A recent study from Sweden found small increases in the risk of two pregnancy complications when ozone levels increased.
Women were slightly more likely to give birth early or to have pre-eclampsia (a pregnancy complication involving high blood pressure) for each small increase in ozone.
The researchers estimated that higher ozone levels appeared at least partly related to one of every 20 cases of pre-eclampsia that pregnant women experience.
"Attend all prenatal appointments."
The study, led by David Olsson, a PhD student at the Department of Public Health and Clinical Medicine at Sweden's Umeå University, looked at possible links between air pollution and poor pregnancy outcomes.
The study included all single children born from 1997 to 2006 in the greater Stockholm area of Sweden, which totaled 120,755 children.
The researchers recorded the rates of babies born early, pregnant women who had pre-eclampsia and babies born underweight. Pre-eclampsia is a potentially dangerous pregnancy complication involving high blood pressure and protein in a woman's urine.
Then these pregnancy outcomes were compared to the levels of ozone and car exhaust that women were exposed to during the first trimesters of their pregnancies. The data on ozone came from two stations in Stockholm, and the data on vehicle exhaust levels came from three stations in the city.
The results were adjusted to account for whether the mothers had asthma or smoked, as well as the women's age, education, weight, family situation, number of children and area of origin. Adjustments were also made for the child's gender and the year the child was conceived.
The overall rate of preterm birth during the study period was 4.4 percent. Overall, 2.7 percent of the women had pre-eclampsia.
The researchers found that women were 4 percent more likely to have pre-eclampsia or to give birth early for every 10 μg/m3 increase in ozone they were exposed to in their first trimester. This measurement refers to how many micrograms of particles are in each cubic meter of air.
Therefore, the more ozone that was in the air during a woman's first trimester, the higher her risk of pre-eclampsia or preterm birth appeared to be, though these risks increased in small amounts.
The researchers estimated that about one of every 20 cases of pre-eclampsia were related to ozone levels.
The researchers did not find any links between vehicle exhaust and pregnancy outcomes, and ozone levels did not seem to show any effect on whether babies were born underweight.
The study was published February 6 in the journal BMJ Open. The research was funded by the Centre for Environmental Research. The authors declared no conflicts of interest.