We have previously written about how more women go into labour earlier during hot summer days, and especially if there is a heatwave.

And now a new study has been able to find that birth rates are as much as five percent higher on days when the temperature reaches 32 degrees Celcius– and above. The study, published by UCLA this week, found that birth on those hot days occurred up to two weeks earlier and 6.1 days earlier on average than it would have otherwise. And this, the researchers concluded, is how climate change is directly affecting the health of babies, with shorter pregnancies posing a risk for both infant health and child development. Babies are considered premature when they are born at 37 weeks or earlier. But while definitively safer for baby, delivery between 37 and 40 weeks is still not considered ideal, as early births of even a few weeks are linked to lower birth weight and even potential cognitive development problems later in life. The UCLA researchers looked at statistics for U.S. birth and climate statistics from 1969 to 1988 and estimated that about 25,000 births were affected by rising temperatures caused by climate change each year. The key finding? Birth rates spiked right around the days the temperature exceeded 32 degrees. And after the hot weather passed, birth rates declined again. “That’s enough to take somebody from what’s considered to be a pretty healthy pregnancy into a ‘we are somewhat worried’ pregnancy,” said Alan Barreca, a UCLA professor of environment and human health and lead author of the study. What the researchers discovered by looking at patterns, was that there is a direct correlation between early deliveries and hot weather. Even scarier, they also predict that by the year 2100, it’s estimated that an additional 42,000 births will be affected per year, which is about one out of every 100 births. The exact reason why women tend to deliver babies earlier in hot weather is not 100 percent clear, the researchers point out, but one theory is that heat could be causing pregnant women to experience added stress on their hearts. Another possible reason is that the level of oxytocin, a hormone involved in the onset of labour and delivery, increases in the body when it’s hot.