Rising heat and humidity during pregnancy could leave millions of children stunted

A study in Science Advances found that extreme heat and humidity during pregnancy can raise the risk of childhood stunting. The findings point to higher danger in humid parts of India and South Asia as temperatures climb.

In Short

• Researchers analysed nearly 200,000 South Asian children and maternal weather exposure
• Humid heat showed stronger effects on growth outcomes than dry heat
• The third trimester emerged as the most vulnerable stage for fetuses

Climate change is increasingly being linked to health problems across the world, but new research suggests that its impact may begin even before a child is born. A study published in the journal Science Advances has found that extreme heat and humidity during pregnancy can affect the growth and development of unborn babies, increasing the risk of stunting in childhood.

Researchers say that rising temperatures combined with high humidity can place significant stress on pregnant women, reducing the supply of oxygen and nutrients to the developing foetus. The findings are particularly concerning for South Asia, where heat waves are becoming more frequent and intense due to climate change.

According to the study, if global temperatures continue to rise at the current rate, an additional 3 to 3.7 million children in South Asia could suffer from stunting by 2050. Most of the data used in the research came from India, making the findings especially relevant for the country.

WHAT DID THE STUDY FIND?

The study analysed data from nearly 200,000 children across South Asia and examined weather conditions during their mothers' pregnancies. Researchers found a clear connection between exposure to high heat and humidity and an increased risk of stunting in children.

One of the key findings was that humid heat appears to be more harmful than dry heat. While high temperatures alone can affect fetal development, the impact becomes much stronger when humidity levels are also high.

In India, different regions experience different types of heat. States such as Rajasthan and parts of western India generally face dry heat, while Bihar, eastern Uttar Pradesh and West Bengal experience hot and humid conditions. The study found that pregnant women living in humid regions may face greater risks.

WHAT IS STUNTING?

Stunting is a condition in which a child does not grow to the expected height for their age. It is usually caused by poor nutrition during early development and can have long-term consequences.

According to Dr. Himanshu Bhadani from the Department of Pediatrics at AIIMS Delhi, stunting is not just about a child's height. Children who are stunted may also have weaker immune systems, lower learning abilities and an increased risk of health problems later in life.

Stunting affects millions of children worldwide and remains a major public health challenge, particularly in low- and middle-income countries.

HOW DOES HEAT AFFECT AN UNBORN BABY?

During extremely hot weather, the human body works harder to maintain a normal temperature. Pregnant women are especially vulnerable because pregnancy already places additional demands on the body.

Exposure to intense heat and humidity can increase the risk of dehydration, heat exhaustion and heat stroke. These conditions can reduce blood flow to the placenta, the organ that supplies oxygen and nutrients to the baby.

When the placenta does not function efficiently, the foetus may not receive enough nutrition to support healthy growth. Over time, this can affect the baby's development and increase the likelihood of growth-related problems after birth.

WHY IS HUMIDITY A MAJOR CONCERN?

Researchers found that humidity plays a critical role in increasing the harmful effects of heat.

Normally, the body cools itself through sweating. However, when humidity is high, sweat does not evaporate easily, making it harder for the body to cool down. As a result, body temperature can remain elevated for longer periods.

The study found that exposure to hot and humid weather during pregnancy was linked to a 5.1% reduction in height-for-age outcomes among children. In comparison, when only temperature was considered and humidity was excluded, the impact was much smaller at 1.3%.

These findings suggest that humidity significantly increases the health risks associated with extreme heat.

THE FINAL MONTHS OF PREGNANCY ARE MOST CRITICAL

The research showed that the risk is highest during the third trimester, which spans from around the 28th week of pregnancy until birth.

This is the stage when the baby experiences rapid growth and requires large amounts of nutrients and oxygen. Any disruption during this period can have lasting effects on development.

Scientists found that exposure to extreme heat and humidity during these final weeks may have the strongest influence on a child's future growth.

WHICH AREAS ARE MOST AT RISK?

The study identified several parts of India where pregnant women may face greater danger due to the combination of high temperatures and humidity.

States such as Bihar, West Bengal and eastern Uttar Pradesh were highlighted as particularly vulnerable because they regularly experience humid heart conditions.

As climate change continues to intensify, researchers believe that these regions could see a higher number of children affected by stunting unless protective measures are taken.

WHAT CAN BE DONE?

Experts say that protecting pregnant women from extreme heat should become a public health priority. This could include ensuring access to cool environments, encouraging adequate hydration, reducing outdoor exposure during peak heat hours and improving awareness about heat-related risks during pregnancy.

Researchers also stress that long-term solutions must address climate change itself. Without action to reduce global warming, rising temperatures and humidity levels could place future generations at greater risk.

The study serves as a warning that climate change is not only affecting weather patterns and ecosystems but may also be shaping the health of children before they are even born. As temperatures continue to rise, experts say protecting pregnant women could become one of the most important steps in safeguarding the health of future generations.

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