Women at Risk of Early Births due to Increasing Temperatures
Wed, April 14, 2021

Women at Risk of Early Births due to Increasing Temperatures

Previous studies have established the adverse effects of rising temperatures on people—old and young alike—but it seems like the environmental crisis also impacts even those in the womb / Photo by: Max Pixel

 

Previous studies have established the adverse effects of rising temperatures on people—old and young alike—but it seems like the environmental crisis also impacts even those in the womb. A new study published in the journal Nature Climate Change found that the increasing climate may increase the chances of premature labor of up to three weeks earlier.

Normal pregnancies normally last up to 40 weeks and being born a week or two earlier may not seem so concerning. But children who are born two or three weeks before their due date, qualifying them as "early term," are at a higher risk of respiratory problems in later childhood.

 

Climate Change on Pregnancy

Premature babies are infants who are born at 37 weeks or earlier, although being born between 37 and 40 weeks—considered the normal duration of pregnancies—is not ideal either, according to Time. It says this is because late-term births are linked to lower birth weight and may possibly contribute to problems in cognitive development in later life.

A lot of factors can come into play that could result in a healthy pregnancy coming into an early term, and one of which is extreme heat. This is the effect that researchers wanted to understand in their analysis of temperature and birth rate records. They used a data set of daily temperature and birth rates in counties across the US from 1969 to 1988.

While the record used was rather old, researcher Alan Barreca said it provided them with the "most thorough information" as the vital statistics system became warier of information given to the public in 1989 "in order to make it hard to identify individuals precisely by place or date of birth."

Their analysis found that the birth rate per 100,000 women increased by 0.97 when temperatures reached or exceeded  32.2ºC (90ºF). Comparing those to days when temperatures were between 16-21º C (60-70º F), the researchers found that birth rates were lower by 5%.

They also found a "smaller, but still significant" rise of 0.57 additional births per 100,000 women on days when temperatures ranged from 26.7-32.2º C (80-90º F).

An Undercount

Increasing birth rates of up to 5% on hot days may not seem like much, but Barreca and his colleagues estimate that an average of 25,000 babies a year are born prematurely in the US from 1969 to 1988 due to warm temperatures. That number sums up to a loss of over 150,000 gestational days every year in the US over two decades—which researchers believe is an undercount, CNN reports.

The study found that the average reduction in pregnancy duration is 6.1 days, but certain cases see babies being born up to weeks earlier than they should. These results are concerning, but they don't explain how extreme heat and early births are associated with each other.

Research on animals shows that heat stress causes the mother to increase its oxytocin production. Human mothers speed up the ripening of the cervix with the rise of this neuropeptide, leading to successive dilation during labor. CNN adds that another theory could be that extreme heat causes cardiovascular stress and thus stimulates earlier deliveries.

The study estimates that another 250,000 gestational days will be lost every year by the end of the century if climate change grows more severe.

Both the mother and the child face negative outcomes with rising temperatures. Previous research shows that mothers are at a higher risk of preeclampsia, hypertension, and other health problems during hot days while dramatic maturation of the brain and rapid physical growth occur during an infant's last week in the womb in the same condition.

Babies who are born earlier than their due date have a higher risk of developing diseases like asthma, developmental delays, and being hospitalized early in life.

Increasing birth rates of up to 5% on hot days may not seem like much, but Barreca and his colleagues estimate that an average of 25,000 babies a year are born prematurely in the US from 1969 to 1988 due to warm temperatures / Photo by: Pexels via Wikimedia Commons

 

Become a Bigger Issue

Current statistics show about 450,000 babies are born too soon in the US alone. Worldwide, 15 million infants are born prematurely—that's 1 in 10 babies, according to parenting site VeryWell Family. It adds that most preterm births are unknown (45%-50%) and over 80% of these incidents are not expected.

The World Health Organization says it remains unclear how or why preterm birth occurs and whether it is the result of the interaction of "several pathways or the independent effect of each pathway."

"Causal factors linked to preterm birth include medical conditions of the mother or fetus, genetic influences, environmental exposure, infertility treatments, behavioral and socioeconomic factors, and iatrogenic (related to medical examination or treatment) prematurity," it adds.

Premature births are likely to become a bigger problem not only in the US, but also around the world as global temperatures continue to rise. Since the period the data set was recorded, there have many more record-breaking hot days and the climate crisis is expected to bring more in the future—unless the world decreases its carbon emissions and prevents further temperature rises.

The study found that air conditioning can help reduce the chances of premature births due to heat, but this method and the absence of more environment-friendly air conditioners and renewable energy sources will make climate change worse. Air conditioning is also costly, so women from families who can't afford it are put at a financial disadvantage to this important solution.