A new study has raised concerns that babies could be affected by air pollution before they are born - but there are ways for pregnant women to protect themselves.
Oxygen and nutrients are delivered to the foetus by crossing the placenta and through the umbilical cord. The study discovered black carbon particles on the fetal side of the placenta after being inhaled by pregnant women.
It is yet to be determined whether the pollution has an effect on the unborn child.
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"Even if these particles don't get into the foetus necessarily, by affecting the function of the placenta they could have a long-term impact," says associate professor Christine Jasoni from the University of Otago's Anatomy Department.
Experts say there is no need to panic, as there are simple ways to minimise exposure to air pollution.
"On a global scale we have pretty good air quality, so it's nothing to be concerned about here in New Zealand - but that doesn't mean we should be complacent either. There are things we can all do to reduce our exposure to air pollution and improve the environment around us," says associate professor Jennifer Salmond from the University of Auckland's School of Environment.
"If you walk beside queuing traffic, simply crossing the road to walk beside free-flowing traffic can reduce your exposure.
"Step back from the road when waiting at traffic lights, if you avoid congested routes and walk through a park... you get to the endpoint with less pollution in your system."
The pregnant women who lived closest to busy roads had the highest levels of particles in the placenta.
"But this does not mean that there is black carbon in the foetus," Jasoni reiterates.
Salmond's advice can be supported by air quality monitoring equipment.
"[If someone] stands really close to the road, close to a vehicle's exhaust, [we'll] see really high numbers. Whereas standing further back from the road, in a parkland or less congested street, you'll have much lower concentrations of particles," she says.
New Zealanders can also choose public transport or lower pollution transport options, like electric cars.
Exposure to air pollution has been linked to miscarriage as well as premature births and low birth weights, which come with their own long-term health implications.
"The biggest risk is for low birth weight, which significantly increases life-long risk for a collection of diseases including diabetes, cardiovascular disease, asthma and stroke," says Jasoni.
Two main causes of air pollution in New Zealand are traffic emissions and smoke from wood burners.
"In cities like Auckland, traffic emissions tend to dominate for most of the year, whereas in places like Timaru, Alexandra or Queenstown, woodsmoke emissions are more important," says Salmond.
Whether soot particles harm the placenta or foetus remains unknown as more research is needed.
Regardless, reducing emissions is a good thing for the health of everyone.