Heat waves linked to early labor and premature births in new research

HBinge eating is becoming more common and intense, causing increasing health risks worldwide. High temperatures can be fatal and are especially dangerous for people with cardiovascular disease and chronic diseases, but they begin to affect human lives even before birth.

Various studies have identified an increased risk of preterm birth and stillbirth after heat exposure around the world. A new study, published Friday in JAMA network openedconfirmed the association with preterm births on a large scale in a large cohort study that examined more than half of births in the United States between 1993 and 2017. The results shed light on how existing health inequalities may be exacerbated by a worsening climate.

The study looked at more than 53 million singleton births that occurred in the 50 most populous U.S. cities during the hottest months of the year. Looking back at the heat waves between May and September, researchers counted premature births (between 28 to 37 weeks of pregnancy) and premature births (between 37 and 39 weeks) within four to seven days after the peak. During that period there were 2.15 million premature births and 5.8 million premature births.

After a heat wave, which the study defined as four consecutive days in which the average temperature was higher than the local 97.5th percentile, preterm births increased by 2% and premature births increased by 1%. But the distribution of these adverse outcomes was uneven: Mothers who were 29 years or younger, had lower levels of education, and were from an ethnic or racial minority group saw a 4% increase in preterm births and a 3% increase in preterm deliveries. .

“When we say people are experiencing a heat wave, only some people are actually physically experiencing that heat wave,” said Lyndsay Darrow, a professor of epidemiology at the University of Nevada, Reno, who led the study. Some people have better access to air conditioning and the financial resources to pay higher electricity bills, for example, or jobs that don’t require physical activity or working outside the home. “We are concerned about the vulnerabilities within the population, the inequalities between people and the potential risks they face,” she said.

While the data did not provide information on mothers’ jobs or income, indicators such as education, age, or race can be used as loose proxies to understand what factors may be at play. In general, women with less education tend to work in more physically demanding jobs and earn lower wages, as do women who belong to racial and ethnic minority groups. And women of lower socioeconomic status tend to give birth earlier in life.

These inequalities hold true across the world, says Jane Hirst, chair of Global Women’s Health at Imperial College London, who was not involved in the study. “Those who are in the most disadvantaged places in society – which is often entirely women, and especially women who have other intersectionality, such as belonging to a non-dominant ethnic group, a religious minority or a lower caste – they are often the ones they are particularly affected,” she said.

Preterm birth is a leading cause of infant mortality and can have long-term physical and developmental effects. “I think there is concern among the maternal health community that while there have been many gains in saving mothers’ lives and babies, preterm birth has been static over the last decade,” Hirst said. Research like this, she said, shows that “there is a chance that things could actually get worse, despite all efforts.”

Vulnerable populations already have a greater risk of preterm labor and premature birth, regardless of heat exposure. Further research is needed to understand whether the link between heat and preterm birth is driven by temperature peaks alone, or whether heat exacerbates other existing risk factors.

A number of recent studies have also found strong links between high temperatures and adverse pregnancy outcomes. A study published last May in the Lancet Data from eight Chinese provinces shows that the number of premature births could have been reduced by about 15% if pregnant women had been warned to protect themselves from impending extreme heat. Another study published in April found that the risk of miscarriage was double among women in the Indian state of Tamil Nadu who suffered from high occupational heat exposure. They also experienced double the risk of adverse outcomes at birth.

Research has not shown which physiological reactions heat can cause in pregnant women and which can lead to premature delivery. “Some studies have recently shown that extreme heat is associated with an inflammatory cascade that could potentially trigger the induction of labor,” says Darrow.

Hirst, who with her team is investigating the physiological causes of premature and early labor, is investigating whether heat and dehydration can affect blood flow to the uterus, causing labor. But that is just one of many working hypotheses. “Frankly, we still don’t really understand how exposure to a heat wave or extreme heat causes the impacts we’re seeing now,” she said.

Recent studies have shown that exposure to extreme heat can also affect fetal development in other ways, note the authors of a commentary on the study also published Friday opened in JAMA network. For example, extreme heat is associated with an increased incidence of birth defects. And it can cause problems in growth and development, including shorter lifespan and poor reproductive health.

“There is a continuum from the burden of caring for a premature baby to the impact on the earning potential of that premature baby’s parents over their lifetime,” wrote commentary author Shruthi Mahalingaiah, an assistant professor of environmental, reproductive health and women’s health. at Harvard, in an email to STAT. Quantifying this burden will require further research, she said, including following up with the babies to understand how their climate exposure might affect their behavioral health, milestones and cognitive functions.

Along with her co-authors, Mahalingaiah called for a more careful understanding and evaluation of the social and economic implications of climate change. “By not including these implications of preterm and preterm birth in public health assessments,” they write, “we vastly underestimate the effects of heat on public health.”