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If you live in a big city like Madrid and you are pregnant, you will have a better chance of giving birth. At least that is the conclusion reached by researchers from the National School of Health of the Carlos III Health Institute.

The study, led by Cristina Linares and published in the scientific publication Environmental Research, concludes that pollution, traffic noise and temperature during a heat wave could influence in the short term the advancement of preterm births that occur in the Spanish capital.

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The researchers point out that physiological mechanisms associated with stress seem to be the cause that relates noise and temperature to premature births, while it is not clearly established what biological mechanism associated with pollution is capable of influencing pregnant women.

Nearly 50,000 premature births in 8 years

According to data from the National Institute of Statistics and contemplated in the investigation, of the nearly 300,000 births that occurred in Madrid in the period 2001-2009:

• more than 24,000 were babies who did not reach 37 weeks of gestation (premature births);
• More than 20,000 correspond to babies born between 30 and 37 weeks of gestation (very premature births);
• 4,270 correspond to deliveries under 30 weeks of pregnancy (extremely premature deliveries).

Pollution and premature births

The research establishes that particles with a diameter less than 2.5 microns (PM2.5), emitted mainly by diesel vehicles, are related to births that occur before 37 weeks of gestation.

They have proven that one day after a pollution peak occurs, the risk of premature birth increases by 3.7% for every 10 microg/m3 increase in PM2.5 concentration.

Heat waves and very premature births

The temperature in heat waves influences the number of premature births and those called very premature.

One day after a maximum daily temperature above 34ºC is recorded, the risk of premature births increases by 5.2% and very premature births by 4.7% for each degree in which the maximum daily temperature exceeds 34ºC.

Noise and extremely premature births

Noise (70% caused by traffic in a large city) is related not only to premature and very premature births, but there is also a clear statistical association between daytime noise and births that do not reach 30 weeks of gestation (extremely premature).

For every dB(A) that daytime noise increases in Madrid, that same day, the risk of a premature birth increases by 15.4%, by 6.9% that of a very premature birth and by 22.2% that of an extremely premature birth.