Extreme Heat During Pregnancy can Lead to Lifelong Health Issues for the Child

Climate change presents one of humanity’s most pressing public health challenges. Global warming, a central aspect of this crisis, is linked to deteriorating health, especially impacting vulnerable populations like pregnant women and children.

Scientists have previously demonstrated that heat exposure increases the risk of preterm birth and stillbirth. New research continues to reveal concerning associations with adverse outcomes for both mothers and their babies, including congenital abnormalities, pregnancy hypertension, and low birth weight.

One area that has received less attention is the long-term impact of heat exposure during pregnancy on infants. To investigate this, we conducted a comprehensive review of existing research examining the effects of prenatal heat exposure on health and socioeconomic outcomes later in life.

Consolidating Medical Evidence through Comprehensive Analysis

Systematic reviews aim to provide the highest level of medical evidence by compiling and summarizing findings from multiple studies, rather than relying on individual research.

Our findings were unequivocal. They indicated that individuals exposed to excessive heat before birth suffer significant lifelong consequences.

The predominant metric for assessing heat is typically the average air temperature, although certain studies have employed more intricate metrics that account for humidity and other factors influencing individual heat perception.

Our research continues to explore how we define dangerous levels of heat for pregnant women. This is influenced by factors such as location, context, and individual vulnerabilities. Different conditions may have varying harmful thresholds and periods of susceptibility.

We reviewed 29 studies spanning over a century, providing insights into effects across individuals’ lifespans. Some studies closely monitored pregnancies to observe any adverse effects on children, while others used population registries to estimate in-utero heat exposure based on birth date and location.

Impact of Heat Exposure on Pregnancy Outcomes

More than 60% of these studies took place in high-income countries with cooler climates, where researchers relied on natural fluctuations in heat exposure rather than conducting controlled trials. Despite these limitations, the majority of studies found a significant link between increased heat exposure during pregnancy and long-term harmful effects.

Specifically, we observed associations with lower educational attainment and income in later life. For instance, in the US, each extra day with temperatures surpassing 32°C during the first trimester correlated with a $56 decrease in annual income at age 30 (adjusted to 2008 equivalent).

Health effects included elevated risks of heart disease, hypertension, childhood asthma, and pneumonia.Researchers estimated that each degree Celsius increase in prenatal temperature exposure increased the risk of childhood pneumonia by 85%.

Regional Implications of Prenatal Heat Exposure

In Africa, higher prenatal heat exposure correlated with increased childhood malnutrition risk, while in the US, studies linked it to higher odds of obesity.

Mental health was also impacted, with heightened risks of eating disorders and schizophrenia observed. This suggests that prenatal heat exposure could be a contributing factor to the well-documented association between birth month and mental illness risk.

These effects seem to lead to a correlation with reduced life expectancy, as researchers found that individuals exposed to higher prenatal heat had shorter lifespans.

In subgroup analyses, studies indicated that these conditions may have a more adverse effect on female fetuses.

Understanding the mechanisms behind these effects across various body systems was a critical focus of our research. We leveraged expertise in human development, ongoing studies investigating the direct impacts of heat on pregnant women, and insights from animal research.

We propose that heat during pregnancy affects the unborn baby through multiple pathways, including:

• exacerbating maternal health conditions like pre-eclampsia and diabetes,
• directly influencing fetal development, particularly the nervous system (which can lead to birth defects),
• increasing the likelihood of preterm birth and other birth complications,
• directly altering the fetal DNA through epigenetic changes, a mechanism that enables rapid adaptation to the environment by modulating gene expression.

Telomere Shortening in Prenatal Heat Exposure

One study even documented the shortening of telomeres in fetuses, which are the biological markers of lifespan linked to our genetic clock.

There is an urgent need for further research in this area to fully comprehend how and why these effects manifest.

Despite the constraints in research, our findings are alarming and underscore the need for prompt action at individual, community, and global levels to safeguard pregnant women and their unborn babies from heat.

We have a responsibility to advocate for those without a voice, who are not responsible for this public health crisis and are likely to suffer its most severe consequences because we have not taken action.

Read the original article on: Science Alert

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