Air Pollution and Heat Linked to Delayed Births

Exposure to air pollution and extreme heat can lead to prolonged pregnancy or delayed birth, resulting in pregnancies lasting over 41 weeks. Typically, a normal pregnancy lasts about 40 weeks.

This finding comes from the study “Maternal climate-related exposures and prolonged pregnancy: Findings from a statewide population-based cohort study in Western Australia,” published in Urban Climate Journal in February 2025.

Researchers analysed data from 393,384 births in Western Australia between 2000 and 2015 to investigate how climate factors, such as air pollution and extreme temperatures, might be associated with longer pregnancies (those extending beyond 41 weeks). They examined air pollution (measured by PM2.5) and the Universal Thermal Climate Index (UTCI), which measured heat stress.

The study concluded that higher levels of air pollution and extreme temperatures were correlated with an increased likelihood of prolonged pregnancy, with specific stages of pregnancy being more sensitive to these environmental exposures. Specifically, each increase in air pollution by 1 μg/m3 was linked to a 6% higher chance of prolonged pregnancy, and exposure to extreme temperatures was associated with even higher risks.

This study of 393,384 births at 37 weeks or more, 47,380, or 12%, resulted in prolonged pregnancy (PP). Of the small share of women who experienced prolonged births, the study identified vulnerability factors as first-time mothers, older mothers aged between 35 and 39, those living in cities, mothers of male babies, and pregnancies with complications.

This study is the first to examine the relationship between climate-related factors like air pollution, temperature stress, and prolonged pregnancy (PP). Researchers note that the 12% of PP cases in the study could be an underestimate, as some pregnancies that might have ended as PP were likely induced or delivered by C-section.

For PM2.5, the likelihood of PP decreased slightly during the early months of pregnancy, but the risk increased as the pregnancy progressed, especially after the fifth month. Cumulative exposure to PM2.5 during pregnancy showed a stronger association with PP.

For the Universal Thermal Climate Index (UTCI), both low and high levels of heat stress were linked to PP, with the highest risk at the most extreme heat levels (99th percentile). PM2.5 exposure increased the chances of PP more in moderate heat conditions

This is the first study to examine the links between climate-related exposures, such as air pollution and temperature stress, and prolonged pregnancy. It suggests that air pollution and temperature stress can also increase the risk of prolonged pregnancy and other pregnancy health outcomes.

The study provides the first evidence to show how air pollution and temperature stress are linked to longer pregnancies of 41 weeks or more. Climate-related factors can shorten pregnancy, but they can also extend births by affecting the body’s hormones and immune systems.

The study recommends that more research is needed to understand better how climate change factors impact pregnancy duration, as prolonged pregnancy can harm both the mother and child and strain the healthcare system.

Climate adaptation interventions, including specific policies and regulations aimed at improving air quality and public health initiatives to protect pregnant women and their unborn children from extreme climate or weather conditions, may help reduce this risk.