High Ambient Temperatures in Pregnancy Related to Childhood Leukemia Risk

A possible link between high ambient temperatures experienced by pregnant women and the later incidence in their children of pediatric acute lymphoblastic leukemia (ALL) is likely robust, according to the results of a new published investigation. The data suggest a particular risk when such temperatures occur in early pregnancy, authors noted.

In The Lancet Planetary Health,¹ the investigators said that not only is childhood ALL the most common malignancy in children, but its incidence is increasing. In the US, the leukemia disproportionately affects Latino children. Additionally, climate change has made high ambient temperatures more common, and they are known to be linked with risk of adverse pregnancy outcomes, especially in racial and ethnic minority groups.²

The authors’ data analysis indicated that the strongest association between risk of childhood ALL and high ambient temperature was when the latter occurred in gestational week 8, during which a 5 °C increase was associated with an OR of 1.07. A slightly larger effect was seen among Latino children (OR, 1.09) than among non-Latino White children (OR, 1.05).

In this analyis, when results were stratified by age of onset, there was a strong association between high ambient temperature in pregnancy and risk of early-onset childhood ALL | Image Credit: Studio Romantic-stock.adobe.com

More research studies that replicate these findings and that investigate the mechanistic pathways that could be involved in the ambient temperature-childhood ALL relationship would help inform mitigation strategies, the investigators stated.

Data Details

The authors of this observational study used California data: birth records (1982-2015), records of children 14 years and younger diagnosed with ALL (1988-2015; n = 6258), and matched controls (n = 307,579). Only gestational weeks occurring in the warmest time of year—May through September—were considered, they stated, and the ambient temperature-childhood ALL relationship was adjusted for confounders, including humidity and air pollution.

Of the total 313,837 individuals included, most were male (55.7%) and of Latino ethnicity (55.7%).

The team’s main analysis found little to no association of ambient heat in the prepregnancy period with risk of childhood ALL, they said, and the results of one of their sensitivity analyses indicated that residual confounding due to risk factors related to residential address was unlikely to explain the results of the main analysis.

Also, differences were seen depending on when childhood ALL was diagnosed: When results were stratified by age of onset, the team observed a strong association between high ambient temperature in pregnancy and risk of early-onset childhood ALL, but not late-onset disease.Previously, other work demonstrated that early-onset cALL vs later-onset cALL is more strongly associated with fetal insults.

Air quality makes a difference as well, with the positive association between exposure to high ambient temperature and risk of childhood ALL being more pronounced at higher air pollution levels. So, although it might be extremely difficult at this point to prevent high ambient temperatures, efforts made to reduce air pollution could help attenuate the association between heat exposure in pregnancy and cALL, the authors stated.

Latino Populations Affected More

Why was the association between high ambient temperature and childhood ALL risk more marked amongLatino than among non-Latino White individuals? To find out, the results would first need to be replicated, and then, the authors speculated, “such differences might reflect disparate exposure to heat due to occupation and residence, or higher sensitivity to heat due to comorbidities.”

They also pointed out that the critical window in the non-Latino White group tended to expand further into the prepregnancy period compared with the Latino group, for reasons that are unclear.

“Hypothetically, if non-Latino White women are less exposed to ambient heat than Latino women, a longer period of exposure might be necessary to trigger the biological processes associated with leukemogenesis,” they suggested.

References

1. Rogne T, Wang R, Wang P, et al. High ambient temperature in pregnancy and risk of childhood acute lymphoblastic leukaemia: an observational study. Lancet Planet Health. 2024;8(7):e506-e514. doi:10.1016/S2542-5196(24)00121-9

2. Chersich MF, Pham MD, Areal A, et al; Climate Change and Heat-Health Study Group. Associations between high temperatures in pregnancy and risk of preterm birth, low birth weight, and stillbirths: systematic review and meta-analysis. BMJ. 2020;371:m3811. doi:10.1136/bmj.m3811