Despite such limitations to studying these effects, “we are getting more and more consistent signals that particles are related to these birth outcomes and they may affect prenatal development,” says Beate Ritz, an environmental epidemiologist at the University of California, Los Angeles. She has studied the connection between particulate matter and birth weight in California since the 1990s, but was not involved in the latest analysis.
Epidemiologists are concerned that some of the effects of a mother's exposure to air pollution may not be seen until several decades after her children are born. “If you think of what is happening in China, that doesn’t bode very well,” says Ritz, referring to recent reports of dangerous air-pollution levels in some Chinese cities. For example, in late January, the 24-hour average reading for PM2.5 in Beijing reached more than 460 μg m–3 according to the US Embassy there; China’s Ministry of Environmental Protection reported a lower figure of around 350 μg m–3.
The World Health Organization recommends that countries establish rigorous air-pollution standards of an annual mean of 10 μg m–3 for PM2.5 and 20 μg m–3 for PM10. The US Environmental Protection Agency recently strengthened its annual PM2.5 standard by decreasing it from 15 μg m–3 to 12 μg m–3. The agency estimates that meeting this standard will provide health benefits worth between US$4 billion and $9.1 billion annually by 2020.
“The impacts of air pollution on pregnancy have not been considered when setting up the regulations,” says Dadvand. “Now is the time to start thinking about it.”