Heatwave Study of 36.6 Million Births Reveals Surge in Premature Deliveries Amid Rising Temperatures

Extreme heat increases the risk of premature birth, according to a new study analyzing 36.6 million births across 250 cities and regions in 13 countries between 1979 and 2019. The research, published in the journal Environment International, suggests that rising temperatures linked to climate change could contribute to more babies being born before term, with potentially serious health consequences that can last throughout life.

The study comes as France faces one of its earliest heatwave episodes ever recorded in May, highlighting the public health concerns associated with rising temperatures. Researchers note that previous studies on heat and premature birth were often limited to a single city or country, making it difficult to compare results because of different methods. This larger international analysis was designed to provide a clearer picture of the relationship between heatwaves and preterm delivery.

The findings point to a consistent pattern: the risk of premature birth rises as temperatures increase. On a moderately hot day, the risk increases by 2.8%, while extreme heat pushes the increase to 3.8%. Based on the researchers’ calculations, 1.41% of premature births that occurred during summer in the study were attributable to heat exposure. That equals 855 additional premature births per million births.

The study suggests that the impact of heat on pregnancy may be substantial, even greater than some other known risk factors in lower- and middle-income countries, such as maternal smoking. It also shows wide differences from one country to another. Paraguay had the highest rate of heat-related premature births, with 1,347 cases per million births, while Switzerland had the lowest, at 628 per million. These disparities may reflect differences in climate, infrastructure, healthcare access, and broader socioeconomic conditions.

The research also underscores that heat does not affect all women equally. The greatest vulnerability appears to fall on younger mothers, single mothers, women with lower levels of education, and those in more precarious socioeconomic situations. These groups may face greater exposure to heat or have fewer resources to protect themselves during hot weather, increasing the likelihood of a premature birth triggered by extreme temperatures.

Premature birth is a major health concern because babies born too early are at higher risk of death and can face complications that affect them for life. The study adds to growing evidence that climate change is not only an environmental issue but also a maternal and child health issue, with extreme heat emerging as a significant risk factor for pregnancy outcomes.

As heatwaves become more frequent and intense, the findings raise urgent questions about prevention, public health preparedness, and the unequal burden of climate-related health risks on vulnerable populations.