How does exposure to heat during pregnancy affect the lifelong health of children?

Climate change is one of the biggest public health threats humanity has ever faced. Global warming is part of this threat.

In fact, rising temperatures are linked to poor health, especially in vulnerable populations, including pregnant women and children.

Scientists have previously shown that exposure to heat increases the risk of premature birth and stillbirth. New research continues to reveal troubling links to poor outcomes for mothers and their children.

Congenital malformations, high blood pressure during pregnancy, and low birth weight are some of the risks of hyperthermia.

One area that has not received as much attention is the long-term effect that exposure to heat during pregnancy may have on the baby.

To explore this question, researchers conducted a systematic review of all existing research on the effects of heat exposure during pregnancy on health and social and economic consequences later in life.

The results showed that people who were exposed to excessive heat before they were born suffered lifelong disturbing effects.

Long term effects

The review found that the majority of studies link long-term harmful effects to increased heat exposure during pregnancy. In particular, researchers found associations with worse educational performance and lower income later in life.

For example, in the United States, annual income at age 30 decreased by US$56 (in 2008) for each additional day with temperatures above 32°C during the first trimester of a mother's pregnancy.

The results also found adverse health effects including increased risk of heart disease and high blood pressure, as well as asthma and pneumonia in children.

It is estimated that the risk of pneumonia in children increases by 85% for every 1 degree Celsius increase in temperature during pregnancy.

In Africa, the risk of malnutrition in children increased with increased exposure to heat during pregnancy. In the United States, one study found an association with an increased risk of obesity.

Several studies have also shown links to mental illness, including an increased risk of eating disorders and schizophrenia.

In fact, previous research has shown that the month in which a baby is born has long been associated with the risk of mental illness. Research suggests that exposure to heat may be one of the reasons behind this.

These effects appear to culminate in an association with reduced life expectancy, with researchers finding that people exposed to increased heat while in the womb died at younger ages.

They also found that the effects appeared to be worse for female fetuses in studies that explored subgroup vulnerabilities.

The researchers suggest that the effects of heat during pregnancy on the unborn child likely occur through multiple pathways, including:

- Deterioration of maternal health through diseases such as preeclampsia and diabetes

- Directly affecting the child’s development, especially the nervous system (heat can cause birth defects)

- Increased risk of premature birth and other problems at the time of birth

- Directly altering the fetus's DNA: This likely occurs through changes in the epigenetic signature, an evolutionary mechanism that allows us to quickly adapt to our environment by turning genes on and off.

One study even pointed to shortening of fetal telomeres, the biological clock in our DNA linked to our limited lifespan.

There is an urgent need to conduct more research in this area and explore how and why these effects occur.