• The No. 1 cause of infant death in the U.S. — preterm births — may be rising because of the worsening climate crisis.
  • Preterm birth study may help fuel the growing interest by investors in funds that focus on sustainability.
  • The study is the latest research showing that the impact of the climate crisis may have serious negative effects on mothers and infants.

A study of single births in California found that the percentage of babies born before 37 weeks rose significantly when mothers experienced extreme heat during their last week of gestation. 

The Environment International study published in ScienceDirect.com said the length of the heatwave was significant: A duration of four or more days with slightly lower temperatures raised the risk of a preterm birth more than a shorter duration with higher temperatures.

“Extreme heat might make mothers more susceptible to changes in hormones,” lead author Sindana D. Ilango, a graduate student at the University of California, San Diego, told the New York Times. “Dehydration could also play a role. These factors may trigger contractions and earlier birth.”

While raging wildfires and locust swarms are dramatic examples of the climate crisis, this study is the latest research confirming that the effects of global warming may be particularly concerning for the health of mothers, infants, and children. Higher temperatures and more frequent heatwaves also have been shown to result in lower birth rates and a higher likelihood of birth defects.

The study may also fuel the growing appetite for social-impact investing that led U.S. funds with a focus on sustainability to attract a record $20.6 billion of new assets last year, according to Morningstar data. The amount was almost four times more than the previous record flow reached in 2018.

The rate of preterm births in the U.S. has risen over the four years ended 2018 to a rate of 10%, according to the Centers for Disease Control and Prevention. Though the U.S. has a goal of reducing the national preterm birth rate to 9.4%, only 18 states were meeting that target, the nonprofit National Institute for Health Care Management said in December. 

For a child born in 2019, the effects of global warming could be severe if the crisis continues unmitigated, according to a report from the Lancet Countdown. Through early childhood, increased pollution and extreme heat will threaten the lowered immune systems of growing bodies, the report says. Asthma and insect-borne diseases may become more common.

Schoolchildren’s development and their ability to concentrate will be hampered by the physical effects of climate-caused pollution, the report said, while outside the classroom, poor air quality will decrease opportunities to play out-of-doors and stay healthy.

Of course, climate change doesn’t just have adverse effects on the health of children. Increased respiratory and cardiovascular disease, injuries and premature deaths are related to extreme weather events, the CDC says. The climate crisis is also causing changes in the prevalence and geographical distribution of food- and water-borne illnesses and other infectious diseases, and threats to mental health.

Ilango’s study recommended that targeted efforts toward reducing exposure to extreme heat, such as heat warning systems and increased cooling zones, might reduce the percentage of preterm births.