World first study of 1.3 million pregnancies in China warns of a dangerous pollutant that causes pre term births


A world first study into the impact of very fine particulate matter pollution – less than 1 mm (PM1) – on preterm births has been done in more than 1.3 million births in rural and urban areas across China.

The complex study, published in the Journal of the American Medical Association Pediatrics, looked at satellite, land use information and meteorology data combined with home addresses of the women in the study to accurately link PM1 pollution with an increased incidence of preterm births.

The study found that an increase in PM1 of 10 micrograms/m3 over the entire pregnancy led to a 9% increased risk of a preterm birth. In areas of very high pollution (over 52 micrograms/m3) there was a 36% increased risk of preterm births.

Preterm birth is the leading cause of death for neonates, infants and children less than 5 years worldwide. It can also cause long term health problems such as asthma and metabolic disorders.

There are no air pollution standards in any country relating to PM1, (most countries only warns about PM10 and PM2.5) and the authors of the study call for an urgent review of these standards with recommendations such as wearing a mask outdoors when the PM1 pollution levels reach very high level.

The study, led by Dr Yuming Guo from the Monash University’s School of Public Health and Preventive Medicine in Australia, with colleagues at Peking University, and National Research Institute for Family Planning in China, also found that the women exposed to the PM1 most likely to have a preterm birth were:

  • Younger than 20 years when becoming pregnant
  • Come from rural areas
  • Come from a lower socio-economic background (and less likely to afford or wear masks)
  • Involved in farming
  • Overweight before pregnancy
  • Conceived in Autumn, possibly because it is a time when people, particularly in rural areas, are harvesting

With the rapid growth of the economy and expansion of the urban population, China is experiencing serious air pollution problems causing 1.6 million deaths nationwide every year.  Fine particulate matter

with aerodynamic diameter 2.5 mm (PM2.5) has attracted increasing public concern and its adverse health effects have been documented by numerous studies.

PM1, a major part of PM2.5, has seldom been studied despite the fact that PM1 accounts for more than 80% of ambient PM2.5 mass at some locations, particularly in China. According to Dr Guo, due to its smaller particle size, PM1 might be more harmful than PM2.5 and more strongly associated with some health outcomes.

Previous global studies of PM2.5 have been restricted to measurements taken at ground monitoring stations. The current study, used satellite remote sensing data combined with daily ground monitoring to accurately estimate the concentrations of PM1 across China from December 1, 2013 to November 30, 2014.

In December, 2017, the British Medical Journal published a UK study showing that for every 10 percent reduction in PM2.5 - 90 babies are protected against being born with low birth weight in London. The Environmental Protection Agency standard for PM 2.5 is 12 micrograms per cubic meter averaged over three years, and the World Health Organization suggests 10 as a limit.

According to Dr Guo, this latest study in JAMA Pediatrics reveals that there is no real safe level of air pollution regarding preterm births. He said his study, and others, raises concerns over the lack of monitoring of PM1 in the atmosphere in developed and developing countries and the need to provide masks to pregnant women when the levels of PM1 get to a level associated with increased preterm birth risks. “A preterm birth can cause a tremendous strain, long and short term, on both a family and on a country’s annual medical costs – in the US preterm births cost $26.2 billion in medical costs annually. It’s important, in light of these findings, to review pollution standards for PM1 levels to reduce the impact on preterm births,” he said.


The finer the particles, the more difficult they are to disperse — and the deeper they can penetrate into the blood stream, causing more harm.

PM10, which are smaller than 10 microns in diameter, enter the respiratory tract, and have been associated with risks like bronchitis, asthma, and upper respiratory tract infections. PM10 aggravate symptoms of existing diseases more than triggering new conditions. PM2.5 are considerably finer, penetrate into the lower respiratory tract or deeper in the respiratory tract, and the blood stream, causing cardiovascular problems. The spike in these particles over the last two years has prompted doctors to advise patients to leave Delhi temporarily.

PM1, which are so much finer than PM2.5, can penetrate the cardiovascular stream even further, and give rise to lasting conditions, such as predisposing people to heart diseases.