Hotter-than-normal summers are taking a toll on millions of the nation’s pregnancies, according to a new study showing rising preterm and early-term birthrates following heat waves in large metro areas, including Atlanta.
A new study by a group of researchers that included Emory University’s Rollins School of Public Health has found that 4 or more consecutive days of high temperatures — 94 degrees or hotter in Atlanta — can lead to an increase in premature births. Last summer there were two stretches of temperatures in Atlanta hot enough to qualify, according to the National Oceanic and Atmospheric Administration (NOAA).
The study found that following heat waves that last for four days, preterm or premature births — defined as delivery at less than 37 weeks — increased 2%. Early-term births, with delivery at 37 to 38 weeks, increased 1%. Early delivery before the full-term of 39 to 42 weeks is the leading cause of infant mortality along with long-term complications to the child, such as respiratory, cognitive or behavioral issues, the study reported.
The new research might point to trouble for pregnant mothers and their newborns in Georgia, considering the state has one of the worst infant mortality rates in the nation and the NOAA has projected above average temperatures again this summer.
The study found consecutive days of high temperatures over a certain threshold specific to each metro area surveyed — 94 degrees for Atlanta — are particularly risky for mothers younger than 30 and 35 or older; members of racial and ethnic minorities such as Black and Hispanic women; and those with a high school education or less, according to the study recently published in the JAMA Network Open.
Emory’s public health school participated in the research along with an epidemiologist and meteorologist, biostatistics and environmental specialists from the University of Nevada, University of Utah, Yale University, Veterans Affairs Health Care Systems in California and the National Center for Atmospheric Research in Colorado.
The most recent National Climate Assessment also indicates that heat waves have become more common and severe since the 1980s, with record-breaking high temperatures.
While the increase the study found in early births was small, the sample size was large. The study included 53 million births from 1993 to 2017 — a little over half the births recorded during that period for the nation’s 50 largest metro areas. Researchers used birth records to analyze trends during the warm season, May to September.
The new research didn’t specifically mention Atlanta, but the findings are applicable to the city and could have implications for local public health, said Howard Chang, senior author of the study and Rollins’ professor of biostatistics and environmental health.
Atlanta OB-GYN Rachel Shulman cautioned that “the study’s conclusions may be overstated” because they only suggest a modest impact of heat waves on preterm birth.
“Preterm births are a big problem in our field, and this study identifies another possible risk factor for preterm birth: heat,” said Shulman, a maternal fetal medicine specialist with Georgia Perinatal Consultants. “But I have concerns regarding how pregnant women will receive this information, as it is not a modifiable risk factor” and the estimated effect was low.
“I am not seeing, nor do I anticipate seeing a noticeably different preterm birthrate in Atlanta in the short term,” Shulman said.
She also points out limitations of the study: the use of birth records, which provide limited information about the women in the study, the study excluding births prior to 27 weeks, and the lack of data about the impact on infants, such as intensive care admissions and rates of complications after birth.
In response, Chang argued that heat exposure is modifiable through better preparedness at the individual, local or regional levels. He said that using U.S. birth records are more reliable than other data because all live births are included. “A study based only on, say, medical records at a hospital will likely have some biases so that the results may not be generalizable.”
When it comes to the 27-week cut off, Chang said “extremely preterm births are more likely due to congenital anomalies and intrauterine infection. So physiologically, we don’t believe heat waves will cause very early preterm.”
He said that evaluating impact is “somewhat subjective. I think a 2% increase is meaningful given the increasing frequency of heat waves.”
Atlanta OB-GYN Andrea Braden offered a similar perspective. She said that while a 1% to 2% rise in early births “may not seem like a lot, those numbers add up quickly when you consider that the study population included over 53 million births. That’s over a million births affected.”
Multiply that figure by the health care costs associated with preterm birth, said Braden, medical director of the Atlanta Birth Center. The March of Dimes pegs the economic cost at $65,000 a year in Georgia, which includes medical, educational, and lost productivity. “You can understand why these ‘modest increases’ translate into huge health economic impacts.”
The preterm birthrate in Georgia is nearly 12% compared to the national average of about 10%, the March of Dimes reports. Meanwhile, about 38% of infant deaths in the state are related to early delivery compared to about 36% nationwide.
She said the correlation between heat and early birth should lead to maternity care practices that help protect those at highest risk.
Chang said the new research about heat and births was consistent with previous findings using data from the 1980s. So much has changed since then, including the prevalence of air conditioning and awareness about temperature, but also the rising cost of energy, he said.
Among its limitations, the study didn’t include rural areas, where mothers may be more vulnerable to extreme heat because they don’t have access to air conditioning. The research also doesn’t say how to reduce heat exposure, but only identifies those who are more at risk. “We need to figure out what targeted intervention should be. I think there’s a lot we can do,” he said.
“If we know the heat waves are dangerous, we have the potential for better prevention with efforts by physicians or family,” Chang said. For example, friends and family can check in on pregnant mothers to ensure they have water.
Public health officials, city planners and policymakers can also help those at risk of extreme heat, he said. State health departments could build cooling stations, provide energy subsidies or financial aid to those who need it.
Nancy Nydam, spokesperson for the Georgia Department of Public Health, said high temperatures can put pregnant women at greater risk of heat stroke, heat exhaustion, and other heat-related illnesses.
“Their bodies have to work harder to keep both mother and baby cool. Heat can also lead to dehydration so drinking plenty of water can help prevent overheating, dizziness and fainting.”
It’s important for pregnant women to know signs of pregnancy complications and the symptoms of heat-related illness, Nydam added. “They should talk to their obstetrician or health care provider if they have questions or concerns.”
How to keep cool in the heat
· Limit direct exposure during the hottest time of the day, 11 a.m. to 4 p.m., and conversely, time your activities for the early morning or late evening
· Hydrate when you have to be outside. The American College of Obstetrics and Gynecology recommends pregnant women consume 64 to 96 ounces (8 to 12 cups) a day.
· Use a personal fan or cool compress on the back of your neck or other parts of the body
· Use a hat to provide shade or stay in a shaded area when outside
· Being in the pool helps cool body temperature as long as it’s not in direct sunlight
Source: Dr. Rachel Shulman, Georgia Perinatal Consultants
The Centers for Disease Control and Prevention in Atlanta also offer advice on heat and pregnancy.
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