Air Pollution and Premature Births: What Studies Reveal

How Air Pollution and Premature Births Are Linked

Air pollution is no longer just an environmental issue—it’s also a growing public health threat, especially for pregnant women and newborns. A new study from Emory University in the United States has revealed how exposure to polluted air during pregnancy can lead to premature and early-term births, putting both mothers and babies at serious risk.

To understand this problem, it’s important to know what these terms mean. A premature birth, or preterm birth, happens when a baby is born before 37 weeks of pregnancy are completed. An early-term birth refers to babies born between 37 weeks and 38 weeks and 6 days. Both conditions can lead to serious health problems, particularly if the baby is born much earlier than expected, such as difficulty in breathing, poor growth, or long-term developmental delays.

But what exactly in the air is causing this harm to pregnant women and their babies? The answer lies in a specific type of toxic air pollutant known as PM2.5.

What is PM2.5 and Why Is It So Harmful?

PM2.5 stands for Particulate Matter that is 2.5 micrometers or smaller in diameter—about 30 times thinner than a human hair. Because of their tiny size, these particles can bypass the body’s natural filters, reaching deep into the lungs and even entering the bloodstream, where they can disrupt critical bodily functions.

These harmful particles are mainly released from:

• Vehicle exhaust (cars, trucks)

• Industrial emissions (factories)

• Burning of coal, wood, or crop waste

• Wildfires

Because of their reach inside the human body, PM2.5 particles are especially harmful to pregnant women, whose bodies are undergoing constant changes to support their growing babies.

How PM2.5 Affects Pregnant Women and Increases Risk of Premature Birth

Donghai Liang, PhD, (left), associate professor of environmental health at Emory University's Rollins School of Public Health, led a study that identified tiny particles in air pollution that are associated with negative birth outcomes. — Emory University

The Emory University study found that even brief exposure to high levels of PM2.5 during pregnancy can cause biological disruptions that may trigger early labor and premature delivery. This is because the particles interfere with natural chemical processes in the mother's body that are crucial for maintaining a healthy pregnancy.

Two key substances affected by PM2.5 exposure are:

1. Cortexolone – A glucocorticoid (a type of steroid hormone) made by the adrenal glands. It helps control inflammation, regulate metabolism, and support the immune system.

2. LysoPE (Lysophosphatidylethanolamine 20:3) – A lipid molecule that plays a vital role in cell structure and communication.

When PM2.5 alters the levels of these substances, it disrupts hormone balance and cellular function, increasing the chances of premature labor and complications during childbirth.

Other Body Functions Disrupted by PM2.5

Beyond hormone imbalance, the study also found that PM2.5 exposure affects essential metabolic processes that support fetal development:

• Protein digestion and absorption – Vital for providing the baby with nutrients needed for growth and development.

• Aromatic amino acid metabolism – Affects the baby’s brain development, immune function, and cell repair mechanisms.

These disruptions can have long-term consequences on the child’s overall health, even if they are not born extremely early.

Risks Associated with Air Pollution and Pregnancy

One of the most dangerous aspects of air pollution is that it affects not just the mother, but also the foetus, which receives oxygen through the mother's bloodstream. When a pregnant woman inhales polluted air, the contaminants can reach the developing baby.

Research has shown that exposure to outdoor air pollution before conception or during the early months of pregnancy can lead to:

• Premature birth

• Birth defects of the brain and spine

• Low birth weight

• Increased vulnerability to infections after birth

The effects are not only immediate but can also extend into childhood and adulthood, making this a multi-generational health risk.

Miscarriages and Fertility Problems

Alarmingly, air pollution has been linked to an increased risk of miscarriages. Studies show that raised levels of nitrogen dioxide—a common traffic-related pollutant—can increase the risk of pregnancy loss by 16%. Even more concerning is evidence that air pollution can be as harmful as smoking in increasing miscarriage risk.

One study found that exposure to ammonium sulfate during pregnancy could result in stillbirths and birth defects. Sulfate comes primarily from coal burning, while ammonium is released through agriculture, automobile emissions, and animal waste.

In addition to pregnancy loss, air pollution has also been associated with fertility issues in both men and women. This includes reduced sperm quality, menstrual irregularities, and difficulty conceiving.

Low Birth Weight

A healthy baby typically weighs between 2.5 to 3 kilograms at 38–40 weeks of gestation. Babies weighing under 2.5 kg are considered to have low birth weight—a condition associated with poor health outcomes later in life.

Exposure to air pollution significantly increases the risk of low birth weight, though it remains unclear which trimester is most vulnerable. Notably, ozone, a gas produced from vehicle exhaust and industrial fumes, has been linked to low birth weight when pregnant women are exposed to it.

Preterm Births and Their Global Impact

Children born prematurely face long-term challenges, including respiratory issues, learning difficulties, and growth problems. According to a major study by the Stockholm Environment Institute (SEI) at the University of York, air pollution contributes to nearly 3 million preterm births each year—that’s 18% of all premature births globally.

This shows that air pollution is not just a local problem, but a global health threat, particularly in highly polluted regions like India.

Other Long-Term Health Effects in Children

Autism

Emerging evidence also links air pollution to developmental disorders. A Harvard study found that pregnant women exposed to high levels of particulate matter pollution during their third trimester were twice as likely to give birth to a child with autism. While there is no cure for autism, early detection and support can help manage symptoms—but prevention through cleaner air is even better.

Asthma

Asthma, a chronic and recurring wheezing condition, is worsened by air pollution. Pregnant women with asthma are at risk of developing preeclampsia, a condition involving high blood pressure and impaired liver and kidney function. Worse still, untreated asthma can reduce oxygen supply to the baby, leading to low birth weight or premature birth.

Studies have also shown that babies exposed to air pollution in the womb have a higher chance of developing asthma later in life.

Why This Is Especially Concerning for India

This problem is far worse in India, which consistently ranks among the countries with the highest levels of PM2.5 pollution, particularly in cities and industrial regions. The average PM2.5 concentration in India is 60.15 micrograms per cubic meter (µg/m³)—over 12 times higher than the World Health Organization's safe limit of 5 µg/m³.

The result? Air pollution is directly linked to around 217,000 stillbirths in India every year.

To clarify:

• A stillbirth is the death of a baby before or during delivery after 20 weeks of pregnancy.

• A miscarriage, on the other hand, usually happens before 20 weeks.

These numbers show the urgent need for action, especially in regions with high pollution and limited healthcare access.

Health Risks for Premature and Early-Term Babies

Being born too early puts babies at a high risk of medical complications. In fact, premature birth is the leading cause of death among children under the age of five worldwide.

Common complications for preterm babies include:

• Cerebral palsy – Affects movement and coordination.

• Respiratory distress syndrome – Caused by underdeveloped lungs.

• Growth problems, learning disabilities, and frequent infections.

Even babies born just before full term (early-term) can suffer from:

• Feeding issues

• A weakened immune system

• A higher chance of hospital admission in the early weeks of life

What Is India Doing to Help Pregnant Women?

To reduce these risks, the Indian government has implemented several maternal and child health programs aimed at providing support before, during, and after childbirth:

1. Janani Suraksha Yojana (JSY) – Encourages hospital births among economically weaker sections to reduce maternal and infant mortality.

2. 102 Free Ambulance Service – Offers free emergency transport for pregnant women and newborns.

3. Mission Indradhanush – Provides vaccinations for children under 2 years and pregnant women against preventable diseases.

4. National Health Mission (NHM) – A large-scale effort to strengthen healthcare in rural and underserved areas.

5. Pradhan Mantri Surakshit Matritva Abhiyan (PMSMA) – Offers free antenatal care services on the 9th of every month, including lab tests, check-ups, and counselling.

6. Pradhan Mantri Matru Vandana Yojana (PMMVY) – Gives financial assistance to pregnant and lactating mothers to support safe institutional deliveries.

Which Regions Are Most Affected?

Certain regions of India face both high pollution and poor maternal health outcomes, making them especially vulnerable:

• Delhi often ranks as one of the most polluted cities in the world.

• Uttar Pradesh and Madhya Pradesh have India’s highest maternal mortality rates:

  • Uttar Pradesh: 192 maternal deaths per 100,000 live births

  • Madhya Pradesh: 170 maternal deaths per 100,000 live births

• Bihar, however, has shown improvement:

  • Antenatal check-up coverage has increased from 18.7% to 34.6% in recent years.

Legal Support: Supreme Court’s Ruling on Maternity Leave

In a landmark decision on May 23, 2024, the Supreme Court of India granted maternity leave to a Tamil Nadu government school teacher—even though it was for her third child. Previously, her application had been rejected under Fundamental Rule 101(a), part of the Maternity Benefit (Amendment) Act, 1961.

The Supreme Court overturned the Madras High Court’s ruling, stating that the woman was entitled to maternity leave, despite having two children from a previous marriage. This decision strongly affirmed that maternity leave is a woman’s right, regardless of the number of children.

Maternity Leave as a Reproductive Right

The court further emphasized that maternity leave is part of a woman’s reproductive rights, which are protected under international human rights laws, including the:

• Right to health

• Right to privacy

• Right to equality and non-discrimination

• Right to live with dignity

It highlighted that Article 21 of the Indian Constitution—which protects the Right to Life—also includes the right to health and dignity, thereby covering maternity benefits.

Clarifying the Law: Maternity Benefit Act

Importantly, the court clarified that the Maternity Benefit (Amendment) Act, 2017 does not deny maternity leave for a third child. It only limits the duration:

• 26 weeks of leave for up to two children

• 12 weeks for the third child or beyond

This means that the right to maternity leave still exists, regardless of how many children a woman has—only the length of the leave changes.

Conclusion

The evidence clearly shows that air pollution poses a serious threat to maternal and newborn health, contributing to miscarriages, premature births, low birth weight, and even developmental disorders like autism. With pollutants like PM2.5, ozone, and nitrogen dioxide affecting the body even before conception, urgent action is needed—especially in highly polluted regions like India. While government health programs and legal protections are important steps forward, they must be supported by stronger pollution control and greater public awareness to ensure safe pregnancies and healthier futures for all children.