Long-, short-term heat exposure in pregnancy linked to severe maternal morbidity

Key takeaways:

• High heat and extreme heat exposure during pregnancy, and during the third trimester, increased severe maternal morbidity risks.
• The strength of the associations increased from least to most severe exposures.

During pregnancy, both long-term and short-term heat exposure were associated with increased risk for severe maternal morbidity, researchers reported in JAMA Network Open.

“Existing literature has associated extreme heat exposure with adverse cardiovascular outcomes,” Anqi Jiao, BS, a PhD candidate in the department of environmental and occupational health at the program in public health at the University of California, Irvine, and colleagues wrote. “Given the susceptibility of pregnant women, it would also be meaningful to investigate the underlying relationships between heat and maternal cardiovascular conditions with severe maternal morbidity (SMM), which may help to explain potential associations between heat and SMM and guide a more targeted intervention for minimizing heat-related SMM risks.”

Jiao and colleagues conducted a retrospective population-based epidemiological cohort study of 425,722 singleton pregnancies (mean age, 30.3 years; 26.2% white) from Kaiser Permanente Southern California from 2008 to 2018. Researchers defined moderate, high and extreme heat days as daily maximum temperatures exceeding the 75th, 90th and 95th percentiles of the time series data from May 2007 to September 2018 in Southern California. Long-term heat exposure was measured by the proportions of different heat days during pregnancy and by trimester. Short-term heat exposure was measured by at least 2, 3 and 4 consecutive days during the last gestational week.

The primary outcome was severe maternal morbidity during delivery hospitalization.

There were significant associations between SMM and long-term heat exposure during pregnancy and during the third trimester. High to extreme heat exposure during pregnancy was associated with a 27% increase in SMM risk and exposure during the third trimester was associated with a 28% increased SMM risk.

Increased SMM risks were significantly associated with short-term heatwave exposure for moderate, high and extreme heat exposure. The strength of the associations increased from least severe with daily maximum temperatures less than the 75th percentile lasting for at least 2 days (OR = 1.32; 95% CI, 1.17-1.48; P < .001) to most severe heat exposure with daily maximum temperatures higher than the 95th percentile lasting for at least 4 days (OR = 2.39; 95% CI, 1.62-3.54; P < .001).

In addition, researchers observed greater associations with severe maternal morbidity risks among mothers with lower educational attainment (OR = 1.43; 95% CI, 1.26-1.63; P < .001) or among mothers whose pregnancies began from November to April (OR = 1.37; 95% CI, 1.24-1.53; P < .001).

“These results indicate the potential benefit of targeted interventions to reduce the risk of SMM by mitigating maternal heat exposure, especially among mothers with low socioeconomic status,” the researchers wrote.