Relative high heat exposure increases the likelihood of adverse birth outcomes: multi-country evidence of heat impacts on birth outcomes
1
Wits Planetary Health Research, Wits Health Consortium, Johannesburg, South Africa
2
Wits RHI, University of the Witwatersrand, Johannesburg, South Africa
3
Department of Social Policy and Intervention, University of Oxford, Oxford, United Kingdom
4
Laboratory of Hygiene and Epidemiology, Faculty of Medicine, University of Thessaly, Larissa, Greece
5
Department of Epidemiology, Lazio Region Health Service /ASL Roma 1, Rome, Italy
6
Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden
7
Division of Clinical Epidemiology, Department of Medicine, Karolinska Institutet, Stockholm, Sweden
8
Unidad de Investigacion Clinica y Epidemiologica Montevideo (UNICEM), Montevideo, Uruguay
9
Study Centre for Perinatal Epidemiology (SPE), Brussels, Belgium
10
Department of Infectious Disease Epidemiology and International Health, Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, United Kingdom
11
Wegener Center for Climate and Global Change, University of Graz, Austria
12
Perinatal HIV Research Unit, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
13
South African Medical Research Council Vaccines and Infectious Diseases Analytics Research Unit, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
14
Department of Global Public Health, Karolinska Institutet, Stockholm, Sweden
15
Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom
16
Centre of Excellence for Women and Child Health, Aga Khan University, Nairobi, Kenya
17
Makerere University, Kampala, Uganda
18
Department of Obstetrics and Gynaecology, Muhimbili University of Health and Allied Sciences, Dar Es Salaam, Tanzania, United Republic of
19
Centre of Research in Human Reproduction and Demography (CERRHUD), Cotonou, Benin
20
Centre for Reproductive Health, Kamuzu University of Health Science, Blantyre, Malawi
21
The Aga Khan University, Medical College, East Africa, Dar es Salaam, Tanzania, United Republic of
22
Women’s, Maternal, Neonatal and Reproductive Health (WH) Unit, Department of Health Systems and Services (HSS), Panamerican Health Organization (PAHO), Washington DC, United States
23
MARCH Centre, London School of Hygiene and Tropical Medicine, London, United Kingdom
24
School of Public Health, University of the Western Cape, Cape Town, South Africa
25
Centre for Sexual Health and HIV/AIDS Research (CeSHHAR), Harare, Zimbabwe
26
Liverpool School of Tropical Medicine, Liverpool, United Kingdom
27
Department of Public Health and Primary Care, Ghent University, Ghent, Belgium
28
Public Health and Primary Care, Trinity College Dublin, Dublin, Ireland
Popul. Med. 2026;8(Supplement Supplement 1):A405
ABSTRACT
INTRODUCTION:
Extreme high temperatures pose a growing threat to perinatal health, which is expected to intensify with accelerating climate change. While there is a growing body of evidence documenting heat-perinatal health outcomes, comparing studies worldwide poses multiple challenges, including heterogeneity in study designs and exposure assessment. In this study, we aimed to assess associations between multiple heat metrics and birth outcomes using data from Africa, Europe, and Latin America and the Caribbean (LAC).
METHODS:
Using hospital (11), regional (2) and national (3) registry data, we employed a time-stratified case-crossover design to evaluate the association between short-term (<7 days) heat exposure and birth outcomes (preterm birth [PTB], stillbirth and low Apgar score). We generated country-specific effect estimates and meta-analysed the results for maximum Universal Thermal Climate Index (UTCI). We further compared the association using minimum, mean and maximum of four different heat metrics (temperature, Wet Bulb Globe Temperature, UTCI, and heat index).
RESULTS:
Across 5445771 births, 7.8% were PTB, 0.5% stillbirths and 0.9% low Apgar. In meta-analysis, compared to the 75th percentile of maximum UTCI, the 99th percentile was associated with 1.10-fold higher odds of PTB [95%CI: 1.07-1.14]. We observed stronger heat-exposure associations in hospital-based registries in Africa (OR=1.22 [95%CI:1.05-1.42]) and LAC (OR=1.27 [95%CI :0.90-1.79]) than population-based registries in Europe (OR=1.10 [95%CI: 1.08-1.11]). We observed a 1.08-fold increase in the odds of stillbirth [95%CI: 0.92-1.27] and low Apgar score [95%CI: 1.00-1.17], with higher risks in Africa compared to Europe. All heat exposure metrics were highly correlated, with similar effect estimates observed, but slightly higher effects using UTCI in more humid countries.
CONCLUSIONS:
As one of the largest studies using harmonised statistical approaches, we provide robust estimates of the detrimental associations of heat on multiple birth outcomes, with stronger associations in low- and middle-income settings, highlighting the disproportionate vulnerability of these populations.
Extreme high temperatures pose a growing threat to perinatal health, which is expected to intensify with accelerating climate change. While there is a growing body of evidence documenting heat-perinatal health outcomes, comparing studies worldwide poses multiple challenges, including heterogeneity in study designs and exposure assessment. In this study, we aimed to assess associations between multiple heat metrics and birth outcomes using data from Africa, Europe, and Latin America and the Caribbean (LAC).
METHODS:
Using hospital (11), regional (2) and national (3) registry data, we employed a time-stratified case-crossover design to evaluate the association between short-term (<7 days) heat exposure and birth outcomes (preterm birth [PTB], stillbirth and low Apgar score). We generated country-specific effect estimates and meta-analysed the results for maximum Universal Thermal Climate Index (UTCI). We further compared the association using minimum, mean and maximum of four different heat metrics (temperature, Wet Bulb Globe Temperature, UTCI, and heat index).
RESULTS:
Across 5445771 births, 7.8% were PTB, 0.5% stillbirths and 0.9% low Apgar. In meta-analysis, compared to the 75th percentile of maximum UTCI, the 99th percentile was associated with 1.10-fold higher odds of PTB [95%CI: 1.07-1.14]. We observed stronger heat-exposure associations in hospital-based registries in Africa (OR=1.22 [95%CI:1.05-1.42]) and LAC (OR=1.27 [95%CI :0.90-1.79]) than population-based registries in Europe (OR=1.10 [95%CI: 1.08-1.11]). We observed a 1.08-fold increase in the odds of stillbirth [95%CI: 0.92-1.27] and low Apgar score [95%CI: 1.00-1.17], with higher risks in Africa compared to Europe. All heat exposure metrics were highly correlated, with similar effect estimates observed, but slightly higher effects using UTCI in more humid countries.
CONCLUSIONS:
As one of the largest studies using harmonised statistical approaches, we provide robust estimates of the detrimental associations of heat on multiple birth outcomes, with stronger associations in low- and middle-income settings, highlighting the disproportionate vulnerability of these populations.
| eISSN: | 2654-1459 |
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