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. 2023 Sep 5;6(9):e2332780.
doi: 10.1001/jamanetworkopen.2023.32780.

Analysis of Heat Exposure During Pregnancy and Severe Maternal Morbidity

Anqi Jiao  1 , Yi Sun  1   2 , Chantal Avila  3 , Vicki Chiu  3 , Jeff Slezak  3 , David A Sacks  3   4 , John T Abatzoglou  5 , John Molitor  6 , Jiu-Chiuan Chen  7 , Tarik Benmarhnia  8 , Darios Getahun  3   9 , Jun Wu  1
Affiliations

Analysis of Heat Exposure During Pregnancy and Severe Maternal Morbidity

Anqi Jiao et al. JAMA Netw Open. .

Abstract

Importance: The rate of severe maternal morbidity (SMM) is continuously increasing in the US. Evidence regarding the associations of climate-related exposure, such as environmental heat, with SMM is lacking.

Objective: To examine associations between long- and short-term maternal heat exposure and SMM.

Design, setting, and participants: This retrospective population-based epidemiological cohort study took place at a large integrated health care organization, Kaiser Permanente Southern California, between January 1, 2008, and December 31, 2018. Data were analyzed from February to April 2023. Singleton pregnancies with data on SMM diagnosis status were included.

Exposures: Moderate, high, and extreme heat days, defined as daily maximum temperatures exceeding the 75th, 90th, and 95th percentiles of the time series data from May through September 2007 to 2018 in Southern California, respectively. Long-term exposures were measured by the proportions of different heat days during pregnancy and by trimester. Short-term exposures were represented by binary variables of heatwaves with 9 different definitions (combining percentile thresholds with 3 durations; ie, ≥2, ≥3, and ≥4 consecutive days) during the last gestational week.

Main outcomes and measures: The primary outcome was SMM during delivery hospitalization, measured by 20 subconditions excluding blood transfusion. Discrete-time logistic regression was used to estimate associations with long- and short-term heat exposure. Effect modification by maternal characteristics and green space exposure was examined using interaction terms.

Results: There were 3446 SMM cases (0.9%) among 403 602 pregnancies (mean [SD] age, 30.3 [5.7] years). Significant associations were observed with long-term heat exposure during pregnancy and during the third trimester. High exposure (≥80th percentile of the proportions) to extreme heat days during pregnancy and during the third trimester were associated with a 27% (95% CI, 17%-37%; P < .001) and 28% (95% CI, 17%-41%; P < .001) increase in risk of SMM, respectively. Elevated SMM risks were significantly associated with short-term heatwave exposure under all heatwave definitions. The magnitude of associations generally increased from the least severe (HWD1: daily maximum temperature >75th percentile lasting for ≥2 days; odds ratio [OR], 1.32; 95% CI, 1.17-1.48; P < .001) to the most severe heatwave exposure (HWD9: daily maximum temperature >95th percentile lasting for ≥4 days; OR, 2.39; 95% CI, 1.62-3.54; P < .001). Greater associations were observed among mothers with lower educational attainment (OR for high exposure to extreme heat days during pregnancy, 1.43; 95% CI, 1.26-1.63; P < .001) or whose pregnancies started in the cold season (November through April; OR, 1.37; 95% CI, 1.24-1.53; P < .001).

Conclusions and relevance: In this retrospective cohort study, long- and short-term heat exposure during pregnancy was associated with higher risk of SMM. These results might have important implications for SMM prevention, particularly in a changing climate.

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Conflict of interest statement

Conflict of Interest Disclosures: Drs Avila and Chiu reported grants from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (funding for conduct of study provided to Kaiser Permanente Southern California) during the conduct of the study. Dr Slezak reported grants from Pfizer, ALK, and Dynavax Technologies paid to institution outside the submitted work. Dr Getahun reported grants from Eunice Kennedy Shriver National Institute of Child Health and Human Development (funding for conducting the study was provided to Kaiser Permanente Southern California) during the conduct of the study as well as grants from the US Centers for Disease Control and Prevention (funding for conducting the study provided to Kaiser Permanente Southern California), Hologic (funding for conducting the study provided to Kaiser Permanente Southern California), Garfield Memorial Fund (funding for conducting the study provided to Kaiser Permanente Southern California), and Johnson & Johnson (funding for conducting the study provided to Kaiser Permanente Southern California) outside the submitted work. Dr Wu reported grants from the National Institute of Environmental Health Sciences during the conduct of the study. No other disclosures were reported.

Figures

Figure.
Figure.. Adjusted Odds Ratios (ORs) With 95% CIs of Severe Maternal Morbidity Associated With Exposure to Heatwaves Under Different Definitions During the Last Gestational Week
Models adjusted for maternal age, race and ethnicity, education level, income level, and year of delivery. HWD1, HWD2, and HWD3 are defined as daily maximum temperature >75th percentile lasting for ≥2, ≥3, and ≥4 days, respectively. HWD4, HWD5, and HWD6 are defined as daily maximum temperature >90th percentile lasting for ≥2, ≥3, and ≥4 days, respectively. HWD7, HWD8, and HWD9 are defined as daily maximum temperature >95th percentile lasting for ≥2, ≥3, and ≥4 days, respectively. HWD indicates heatwave definition; SMM20, severe maternal morbidity measured without the blood product transfusion.
See this image and copyright information in PMC

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