Hot, cold temperature exposure before, after birth related to infant lung function

Key takeaways:

• Compared with a median temperature, extreme ambient temperature exposure was linked to reduced lung volumes in infant girls.
• Infant boys did not show the same consistent relationships as girls.

Maternal and newborn exposures to long-term hot and cold temperatures are linked to worse lung capacity in babies, specifically in girls, according to study results published in JAMA Network Open.

“The results of our study should be replicated in other populations and analyses should be continued to investigate whether associations observed at 2 months of age translate into formally diagnosed respiratory diseases at older ages,” Ariane Guilbert, MSc, and Johanna Lepeule, PhD, from the team of environmental epidemiology applied to development and respiratory health at the Institute for Advanced Biosciences in France, told Healio. “However, our findings suggest that pregnant women and their newborns are especially vulnerable and should be advised to protect themselves from both cold and heat. For example, regarding heat, they could limit their physical activities and favor cooler areas. This requires communication and ambitious adaptation policies.”

In a population-based cohort study, Guilbert, Lepeule and colleagues analyzed 343 mother-child pairs (median maternal age at birth, 32 years; 53% boy newborns) recruited between July 2014 and July 2017 to see how maternal and early-life exposure to hot or cold temperatures before and after birth is related to the baby’s lung function.

Through a multiresolution spatiotemporal model, researchers estimated the average, maximal and minimum temperatures at the participants’ residential address each day in order to categorize their exposure to extreme temperatures into percentiles. Temperatures above the 95th percentile represented the hottest temperatures while temperatures below the 5th percentile represented the coldest temperatures and the 50th percentile represented median temperatures, which was used for comparison against the temperatures of extreme heat and cold.

At 2 months old, researchers used tidal breathing analysis and nitrogen multiple-breath washout tests to evaluate infant lung function.

When assessing temperature exposure in relation to lung function, researchers adjusted for two types of exposure in distributed lag nonlinear models: long-term exposure, or during 35 weeks’ gestation and 1 month following birth; and short-term exposure, or within 7 days prior to taking a lung function test.

Heat exposure

Looking at long-term exposure to average temperatures of 24°C (ie, heat exposure) within weeks 20 to 35 of pregnancy and the first 4 weeks following birth against the median of 12°C, researchers found that infant girls had reduced functional residual capacity (39.7 mL; 95% CI, 68.6 mL to 10.7 mL). Further, 24°C vs. the median temperature was also related to a higher respiratory rate (28 breaths/minute; 95% CI, 4.2-51.9 breaths/minute) in these young girls when exposed at weeks 14 to 35 of pregnancy and weeks 0 to 1 after birth. Similar associations were observed for minimum and maximum temperatures.

Researchers found fewer consistent results related to heat exposure and lung function in infant boys. Short-term average and maximum heat exposure was linked to lower functional residual capacity while long-term average and maximum heat exposure was linked to higher tidal volume and lower respiratory rate, respectively.

Cold exposure

Similar to hot temperatures, long-term 1°C or less exposure vs. the median of 12°C in infant girls was linked to reduced functional residual capacity (21.9 mL; 95% CI, 42.4 to 1.3 mL) when exposed during 15 to 29 weeks of pregnancy and an elevated respiratory rate (45.5 breaths/minute; 95% CI, 10.1-81 breaths/minute) when exposed during 6 to 35 weeks of pregnancy and weeks 0 to 1 after birth.

An additional lung function result in infant girls in relation to average cold temperature exposure was reduced tidal volume (23.8 mL; 95% CI, 43.1 mL to 4.4 mL) when exposed in weeks 14 to 35 of pregnancy and the first 4 weeks after birth.

Notably, significant relationships were observed between exposure to minimum, average and maximum cold temperatures with decreased functional residual capacity, decreased tidal volume and increased respiratory rate at varying timeframes in pregnancy in infant girls.

When assessing lung function measures of infant boys exposed to cold, researchers again found no consistent adverse relationships across the different temperature indicators. Short term exposure to minimum or average cold was linked to increased tidal volume and reduced respiratory rate while long-term exposure to average cold was related to greater tidal compared with the median temperature.

Although these results lack consistency compared with infant girls, this does not mean that infant boys are not impacted by extreme temperatures, according to researchers.

“Possible milder effect among boys cannot be ruled out,” Guilbert and Lepeule told Healio.

“Future studies should further investigate the long-term impact of prenatal exposure to temperature on child development in the broad sense, consider both heat and cold (given climate change will lead to global warming but also more frequent extreme temperatures) and look for critical windows of susceptibility,” Guilbert and Lepeule added.

For more information:

Ariane Guilbert, MSc, can be reached at ariane.guilbert@univ-grenoble-alpes.fr.

Johanna Lepeule, PhD, can be reached at johanna.lepeule@univ-grenoble-alpes.fr.