Data Insight: Exploring the effects of hot weather on pregnancy and newborn health — the MAGENTA study

Climate change is resulting in more frequent, intense and prolonged heat events globally, including here in the UK. A comprehensive understanding of the health impacts of these rising temperatures, particularly among vulnerable groups of the population such as pregnant women and infants, is critical to enable the development of evidence-based, effective interventions and policies aimed at adapting and mitigating future climate health risks in a warming world. 

This Data Insight presents early findings and plans for the MAGENTA (Maternal And preGnancy hEalth aNd elevaTed heAt) project, a £2.2 million Wellcome Trust-funded research project led by Swansea University and partnered with the ADR England-funded Kids’ Environment & Health Cohort at University College London. The overarching aim of this project is to provide evidence on whether exposure to higher temperatures during pregnancy is associated with adverse health outcomes for mother and baby.

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What we found

Heat exposure 

Initial exploration of maternal heat exposure patterns by residential area revealed notable spatial heterogeneity within the cohort. Figure 3 (see full publication) illustrates the weekly 5th and 95th percentiles of maximum temperatures experienced by participants, with the differences between percentiles ranging from 2°C to 14.5°C. This considerable variability in temperature exposure, even within the relatively temperate climate of Wales, underscores the importance of assigning exposures at the individual rather than aggregate level.

Analysis of temperature exposures by urban/rural residence defined using the 2011 Rural-Urban Classification revealed notable differences between settings. As shown in Figure 4 (see full publication), mothers residing in urban areas experienced a greater number of days during pregnancy when maximum temperatures exceeded 25°C (the cut-off level used by the Met Office to define heatwaves for the great majority of counties in Wales) compared with those in rural areas. This disparity may reflect the influence of the urban heat island effect, which will be examined in more detail in subsequent analyses.

Outcome measures 

Four outcome measures in this 2022 cohort were examined: gestational age at birth as measured by completed weeks of gestation, maturity category, birth weight in grams and birth size category based on birth weight percentile. Median gestational age at birth for the entire cohort was 39 weeks (IQR 38-40) while median birth weight was 3400 g (IQR 3050-3730). Table 3 (see full publication) shows the breakdown of the cohort by maturity category and birth size category.

Table 4 (see full publication) presents the distribution of maturity categories across deprivation quintiles. Initial analyses indicate that mothers living in more deprived areas were more likely to have a moderate to late preterm birth compared with those living in less deprived areas. This observation is consistent with evidence from national datasets, which report increased preterm birth rates in more deprived populations. Including this table helps illustrate baseline inequalities in preterm birth, providing context for MAGENTA’s key objective of investigating whether socioeconomic disadvantage increases vulnerability to heat during pregnancy.

Why it matters 

Human-induced climate change is contributing to a warmer world, and the UK is already experiencing more frequent and prolonged episodes of high heat, with negative consequences for public health. Understanding the impact of increasing heat on pregnancy is particularly important, as adverse pregnancy outcomes can have lifelong health impacts for both mothers and their children. 

The MAGENTA22 e-cohort presented in this report represents an important feasibility step in the overall MAGENTA project, successfully demonstrating the linkage of anonymised birth records to daily temperature exposures for mothers throughout their pregnancy. Early insights from the MAGENTA22 e-cohort will inform the development of the full MAGENTA e-cohort, which will include all births from 2010 onwards in both London and Wales alongside enhanced bespoke land-surface temperature modelling to better approximate household-level temperature exposures. 

With active public and stakeholder engagement throughout the project through our research midwives, established PPIE group, steering committee and ADR network; MAGENTA will produce actionable recommendations for the public, policy makers and practice to inform future climate health risks and recommendations for adaptation policy and practice.