drooling baby
© Tognopop via Wikimedia Commons
Three month old infant lying on stomach.
A new study suggests climate change causes more women to go into premature labor, though the effect is diminished in warmer climates.
How Rising Temperatures Due to Climate Change are Shortening Pregnancies

BY JEFFREY KLUGER 11:00 AM EST

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To study this effect, Alan Barreca, an associate professor at UCLA's Institute of Environmental Sustainability, and economist Jessamyn Schaller of Claremont McKenna College, analyzed daily temperature and county-by-county birth rates across the U.S. in a two-decade window from 1969 to 1988. That is an admittedly old dataset, but the researchers had little choice.

"In 1989, the vital statistics system started to be more cautious about information it allowed out publicly in order to make it hard to identify individuals precisely by place or date of birth," says Barreca. "They even began masking some counties. So 1969 to 1988 gave us the most thorough information."
In that dataset, the researchers found that on days when temperatures reached or exceeded 32.2ºC (90ºF), the birth rate per 100,000 women increased by 0.97, compared to dates in which the temperature was between 16-21º C (60-70º F). There was a smaller, but still significant, bump of 0.57 additional births per 100,000 women on days that were hot but not quite as sweltering, ranging from 26.7-32.2º C (80-90º F).

"There may even be a third cause," Barreca says, "which is loss of sleep. Minimum temperature on a hot day occurs at night, but it can still be hot enough to disrupt sleep, and that might be an important avenue to early birth."

The effect of heat on pregnancy was less pronounced in hot-weather regions like the desert southwest and the deep south, probably because expectant mothers who live in these parts of the country have acclimated to high temperatures. Income makes a difference as well: greater wealth means a greater likelihood of air conditioning in the home, mitigating the pregnancy-shortening effect of temperature. And since, in the U.S., income often breaks down along racial lines, the study found that African-American mothers are somewhat more likely to experience temperature-related early births than white mothers.

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Read more: https://time.com/5740394/climate-change-early-births/
The abstract of the study;
The impact of high ambient temperatures on delivery timing and gestational lengths

Alan Barreca & Jessamyn Schaller

Evidence suggests that heat exposure increases delivery risk for pregnant women. Acceleration of childbirth leads to shorter gestation, which has been linked to later health and cognitive outcomes. However, estimates of the aggregate gestational losses resulting from hot weather are lacking in the literature. Here, we use estimated shifts in daily county birth rates to quantify the gestational losses associated with heat in the United States from 1969 to 1988. We find that extreme heat causes an increase in deliveries on the day of exposure and on the following day and show that the additional births were accelerated by up to two weeks. We estimate that an average of 25,000 infants per year were born earlier as a result of heat exposure, with a total loss of more than 150,000 gestational days annually. Absent adaptation, climate projections suggest additional losses of 250,000 days of gestation per year by the end of the century.

Read more: https://www.nature.com/articles/s41558-019-0632-4
Sadly the full study is paywalled. But I'm glad the authors pointed out that air conditioning makes a difference.

The solution to this problem, if it exists, is obviously more fossil fuel; cheap energy, a stronger economy with more opportunities for poor people, and greater availability of air-conditioning.