A recent study claimed that birds were shrinking in size due to climate change. However, the effects of climate change on the biology of higher animals may extend to human beings as well, says a new UCLA study. According to the research, climate change is leading to women having shorter pregnancies than their normal terms, which in turn may jeopardize infant health and child development.

The study states that on days when temperatures were above 90F, birth rates were 5 times higher. It also stated that births that took place on those days were nearly two weeks earlier, or on average 6.1 days earlier, than they would have normally.

"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, lead author of the study.

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The link between early birth and hot weather

Using the data on birth rate from the National Vital Statistics System, and climate statistics from the Global Historical Climatology Network, the researchers compared the two parameters to find a connection. They found that there was a sharp rise in the number of births on days the temperatures crossed 90F, and a dip in the numbers after the hot weather passed. Nearly 25,000 births were affected each year they estimated. This led the authors to deduce that the rise and fall pattern of birth rates implied that hot weather causes deliveries to accelerate and shortened gestation.

However, Barreca said that the exact reason behind the link between shorter pregnancies and hotter weather was not certain. Oxytocin is a hormone responsible for the inducing of labour and delivery. The level of oxytocin in the body rises when the temperature is higher, and the researchers speculate that this could a reason behind the phenomenon. Increased stress on the hearts of pregnant mothers could be another reason they posit.

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Access to air conditioning facilities a key factor

Barreca suggests that improved air conditioning facilities could help in alleviating the effects of climate change on pregnancy. However, race and class differences could make the availability of air conditioning difficult for some women. With regard to racial differences, the study found that the effects of higher temperatures were likely to be felt more by black women that white women during pregnancy—with emphasis on further research to understand the exact reason behind the varying risks among women of different races.

"My next question is how we can get air conditioning into low-income households, and at the same time, keep greenhouse gas emissions low," said Barreca pointing out the associated ills of greenhouse gases that are produced by air conditioning systems.

Proven effects of premature birth on infants

The study estimates that around 42,000 births will be affected every year—nearly one in every hundred births, by the year 2100. This further adds to the already proven link between the conditions of and during the period of gestation, and infant health.

Studies have shown that premature birth can result in long-term health concerns. Children that are born due to early deliveries have been found to have cognitive and social difficulties later in life. As adults, they exhibit behaviours associated with higher levels of autism, along with neuroticism, introversion, reduced risk-taking capacity, and agreeableness.

The link between exposure to extreme temperature extremes and its impact on birth outcomes, including gestation period, post-birth stress, stillbirth, and birth weight have also been established through studies.