Rising temperatures due to climate change aren’t only warming oceans and sparking devastating wildfires. As the world gets hotter, women are also having shorter pregnancies than they normally would, putting their children at risk of poorer health and cognitive development, according to a recent study.
Alan Barreca, a UCLA professor of environment and human health, led the study published recently in the peer-reviewed journal Nature Climate Change. The findings showed that birth rates spiked on days when the temperature exceeded 90 degrees Fahrenheit, and decreased after hot weather passed.
Birth rates were 5% higher on days when the temperature exceeded 90 degrees Fahrenheit and births on those days occurred between 6.1 days and two weeks earlier than they normally would.
Researchers analyzed US birth and climate statistics from 1969 to 1988 in 445 different places using birth rate information from the National Vital Statistics System and data from the Global Historical Climatology Network.
The team reported that about 151,000 days of gestation were lost per year during the study's timeframe in the US, based on the average number of hot days. They estimated that about 25,000 births per year took place earlier than they would have without the extreme heat, Quartz reported.
It has not yet been decided if birth rates are an accurate way to determine an association between higher temperatures and early births, according to ABC News.
The study doesn’t explain the direct correlation between extreme heat and earlier births, but exposure to extreme heat is thought to increase the likelihood of delivery by triggering cardiovascular stress or increasing levels of oxytocin, according to CNN.
Mothers face an increased risk of the pregnancy complication preeclampsia, as well as hypertension, and other health problems with higher temperatures. It’s also possible that hot temperatures disrupt sleep, Barreca told Time.
The study also found that hot days have a greater effect on the infants of black mothers than those of white mothers. It takes 30 days after extreme heat exposure for birth rates to return to normal among black mothers.
The effect of heat on pregnancy was less pronounced in hot-weather regions like the Southwest and the Deep South because expectant mothers there might be used to the heat.
Pre-term labor (three weeks or more before the usual 40 weeks) is higher in women who experience poverty — and two-thirds of premature births occur in 15 countries, primarily in India, China, and Nigeria.
Every year 1.1 million premature babies die globally. Babies born early have a higher risk of diseases such as asthma, higher risk of developmental delays, and greater risk of needing to be hospitalized early in life, according to CNN.
Climate change is expected to bring more extremely hot days, which could cause the loss of an additional 250,000 gestational days every year by the end of the century, affecting nearly 42,000 additional births if high carbon emissions continue, the report said.
If efforts to reduce greenhouse gases are made on a global scale, scientists say rising temperatures could be slowed or eventually reversed, which could potentially protect tens of thousands of children around the world.