The effects of climate change are in the headlines a lot these days, from massive wildfires in Australia to urban flooding in Miami. A recent study reveals another disturbing impact to reckon with: Rising temperatures have been linked to an increase in premature births.

The study by scientists at UCLA, published in the journal Nature Climate Change, found that on days when the outside temperature rises above 90 degrees, birth rates increased by 5%. When the temperatures dropped, so did the birth rates.

The findings are significant because a baby’s last weeks in the womb are critical for brain development and physical growth. Babies born early have a higher risk of contracting diseases such as asthma as well as of being developmentally delayed and needing early hospitalization.

The researchers examined 56 million births that took place in various temperatures between 1969 and 1988. Over the 20 years studied, the researchers found that more than 25,000 babies were born prematurely in the United States on days when the temperatures spiked above 90 degrees.

This equates to over 150,000 days total of lost gestation for these babies, a startling loss of precious development time. Of the babies included in the study, on average they were born six days early. But some babies were born as early as two weeks earlier than planned.

Keep in mind that the study looked at a period more than 30 years ago, when the planet’s climate was better than what we face today. The risk of even more babies being unable to complete their full gestational cycle will continue to climb as the planet continues to heat up.