Clinicians should advise pregnant women to limit their exposure to atypically hot or cold weather to reduce the risk for giving birth to a low weight infant, according to a study by the NIH published in Environmental Research.
Pauline Mendola, PhD, of the division of intramural and population health research at NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development, and colleagues examined the medical records of 223,275 births at 12 clinical centers across the United States and linked them to hourly temperature records for the region in which the clinical center was located. Extreme cold was defined as below the 10th percentile of average temperatures for the designated region, while extreme heat was defined as above the 90th percentile.
They found that term infants were 18% to 21% more likely to be of low birth weight – defined as less than 5.5 pounds at birth - if their mother was exposed to extreme cold during either the second or third trimester, while term infants were 257% more likely to be of low birth weight when the mother was exposed to extreme cold over the entire pregnancy. In addition, term infants were 31% more likely to be of low birth weight when the mother was exposed to extreme heat in the third trimester, while term infants were 249% more likely to be of low birth weight when the mother was exposed to extreme heat over the entire pregnancy.
The researchers were unable to determine why extreme high or low temperatures affect birth weight. However, they noted that previous studies have suggested that exposure to heat could increase inflammation and oxidative stress, thus affecting birth weight. Furthermore, blood flow to the uterus could be reduced due to exposure to atypical temperatures, which would deprive the infant of oxygen and nutrients, as well as hinder the placenta’s ability to remove fetal wastes, they wrote.
“Until we can learn more, it makes sense to reduce the amount of time that pregnant women are exposed to extreme hot or cold weather,” Mendola said in a related press release.
Low birth weight increases an infant’s risk for infection and developmental delays in comparison to infants born with a normal weight, according to the researchers.
The researchers previously analyzed the same data in 2016 and determined that extreme temperatures may increase the risk of preterm birth.
Other research from last year suggested that low and very low birth weight are linked to mortality during adolescence. – by Alaina Tedesco
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