A Swedish study found a link between increased exposure to ozone in the first trimester and the occasionally fatal BP condition in pregnancy.
Researchers suggested as many as one in 20 cases - thousands in the UK each year - are being caused by the air pollutant. Mothers with asthma may be particularly vulnerable.
Pre-eclampsia rates have been falling since 1992 due to better management. But the condition, marked by raised BP and protein in the urine during pregnancy, can cause complications and is sometimes fatal.
Researchers from Umea University in Sweden tracked 120,775 pregnancies in Stockholm between 1998 and 2006, and compared medical records to pollution measures.
They found 2.7% of women developed pre-eclampsia, with the risk rising by 4% for every 10µg/m3 rise in ozone levels.
The link was more pronounced in women with asthma, who were 10% more likely to have pre-eclampsia and 25% more likely to have a child born prematurely.
The authors concluded: 'These findings merit further investigation on how exposure to air pollution during early gestation might affect the placenta and lead to adverse pregnancy outcomes.
'A larger proportion of diesel vehicles in our cities is expected to increase both NO2 and O3 levels. The health impact may involve less discussed effects as adverse pregnancy outcomes.'
Around one in 10 pregnant women in the UK develop pregnancy-induced hypertension or pre-eclampsia.
The study was published in the BMJ Open journal.