HEATWAVE AND PREGNANCY: 2024 heat linked to preterm births in Western Visayas, Negros

Extreme heat in April 2024 was linked to an estimated 28 excess preterm births in Western Visayas and 27 in the Negros Island Region, according to a new analysis by Zero Carbon Analytics (ZCA).

Those were the highest counts among the Visayas regions. Central Visayas followed with 23 and Eastern Visayas with 16.

Together, the Visayas regions accounted for 94 excess preterm births, or 16% of the national total.

Nationwide, the heat was linked to an estimated 10% rise in preterm births compared with a typical April. That equals 585 excess preterm births during the 15-day heat event from April 15 to 29, 2024, or around 8 per 1,000 births.

Calabarzon had the most excess preterm births at 103, followed by Metro Manila and Central Luzon. Metro Manila accounted for 82, or 14% of the national total.

Cagayan Valley in northern Luzon had both the largest increase in preterm birth risk, around 15%, and the highest rate, at 12 per 1,000 births. Cagayan province was 4.01 degrees Celsius hotter than normal, and its risk rose by 17%. Caraga in Mindanao had the lowest rate, at 3 per 1,000 births.

During the heat event, the average person in the Philippines experienced temperatures 2.44 degrees Celsius above normal.

ZCA said its regional figures can show where more health service capacity may be needed, including adding heat protection to prenatal care, community maternal health services, and health-system preparedness.

The research group also estimated that 263 preterm births in the Philippines during the April 2024 heat would not have occurred without human-caused climate change.

According to World Weather Attribution (WWA), the heat the Philippines experienced would have been virtually impossible without human-caused climate change. WWA also found that climate change made the heat about 1.2 degrees Celsius hotter in the Philippines.

At 7.7%, the Philippines has a lower preterm birth rate than India or Bangladesh, but its heat exposure has risen the fastest of the three countries.

ZCA cited a May 2025 analysis by Climate Central, which found that climate change caused 30 of the 36 pregnancy heat-risk days the Philippines had each year from 2020 to 2024. That is 83% of the total.

The Philippines ranked seventh in Germanwatch’s Climate Risk Index 2026. India ranked 15th and Bangladesh 13th. ZCA said pregnancy-specific heat exposure in these countries is rising faster than almost anywhere else in the world.

ZCA said it found no heat-specific maternal health guideline or heat action plan for the Philippines.

The country’s Maternal, Newborn, Child Health and Nutrition strategy aims to reduce maternal and newborn deaths through health services. However, ZCA said it was not designed with heat in mind.

The World Health Organization defines preterm birth as the birth of a live infant before 37 full weeks of pregnancy. It is the leading cause of newborn deaths worldwide and is associated with long-term physical, neurodevelopmental, and socioeconomic effects for babies.

Across the Philippines, India, and Bangladesh, ZCA estimated that human-caused climate change caused 10,600 excess preterm births during the April 2024 heatwave alone. The 95% confidence interval runs from 5,100 to 17,700.

Of that total, around 8,830 were in India, 1,479 in Bangladesh, and 263 in the Philippines. These are births that would not have occurred without human-caused warming.

According to WWA, human-caused climate change made the April 2024 heat event around 45 times more likely in South Asia and about 0.85 degrees Celsius hotter there.

In a separate analysis, ZCA compared April 2024 with a typical April. April is already one of the hottest months of the year in the three countries. By that measure, the heat was associated with roughly 16,150 excess preterm births, with a 95% confidence interval of 10,100 to 22,400.

That included a 3.6% increase in preterm births in India, an 11.9% increase in Bangladesh, and a 10% increase in the Philippines.

ZCA said the 10,600 figure is not a share of the 16,150 figure. The 16,150 figure compares the event with the climate of the past three decades, which already includes much of the warming so far. The 10,600 figure compares it with a world without human-caused climate change.

South Asia had the highest preterm birth rate of any region in 2020, at 13.2%. That year, Bangladesh had the highest average rate of any country at 16.2%, with little improvement over the past decade. India’s rate was 13.0%.

The analysis drew on temperature data, preterm birth data, attribution science, and advanced climate models. ZCA said it is the first study to estimate how many preterm births in the three countries were linked to the April 2024 heat, including where the burden fell within each country.

ZCA said it is also the first study to estimate how many of those births can be attributed to human-caused climate change. It also projects how continued global warming could affect preterm births in India and Bangladesh by the middle of the century.

The group said some of the preterm births it counted may not be additional overall, because heat can bring forward a birth that would have been preterm anyway. It added that its results may underestimate the burden from humid heat.

The study found that maternal health policies and heat action plans do not yet consistently protect pregnant women and babies from heat in the Philippines, India, or Bangladesh.

The researchers said better prenatal care, access to cooling, and early warning systems are needed to reduce some of the preterm births caused by climate change.

Exposure to extreme heat during pregnancy is also linked to higher risks of hypertension, gestational diabetes, severe maternal illness, and stillbirth. Droughts, floods, and air pollution from burning fossil fuels pose additional and growing threats to the health of mothers and newborns in the region.

The findings come during another year of unprecedented heatwaves and other extreme weather fueled by climate change, with global warming also strengthening the current El Niño.

COP31 opens next week, and health is among its key priorities. Ahead of the conference, the U.N. climate chief launched a call to address how climate-driven heat affects pregnancy and birth, describing it as “a new faultline in the global climate crisis, and one which is potentially fatal.”

The U.N. climate chief also cited a September 2026 Wellcome Trust survey of 1,000 maternal health care workers in five countries, including India. Seventy-three percent said they had seen more heat-related cases or complications among pregnant women over the past five years. Ninety-two percent said they wanted more training and resources to protect them.

The WHO, the World Meteorological Organization, UNICEF, and UNFPA also recently launched a global framework to track the growing health risks of extreme heat for pregnant women, newborns, and children.

The 2026 Report of the Lancet Countdown on Health and Climate Change, published Oct. 28, 2026, found that many health impacts of climate change are outpacing climate action. It called for climate change to be declared a global health emergency.

Dr. Joanne Bentley-McKune, the report’s lead author and a senior research analyst at ZCA, said: “Climate change is making extreme heat more frequent and intense, raising the risk of preterm birth, which is linked to lifelong health impacts.”

“Our research estimates that the extreme heat of April 2024 may have caused more than 16,000 additional preterm births in India, Bangladesh and the Philippines, compared with a typical April in recent decades. Compared with a world without human-caused climate change, we estimate that more than 10,000 of that month’s preterm births would not have occurred,” she said.

“These impacts will grow as temperatures rise: we project that by mid-century, an ordinary April in India could see even more additional preterm births than the exceptionally hot April of 2024,” Bentley-McKune added.

ZCA projected that for 2041 to 2060, a typical April could bring roughly 15,300 excess preterm births in India, with a 95% range of 6,800 to 28,100. For Bangladesh, the projection is roughly 1,500, with a range of 630 to 2,900. Both figures are compared with an average April from 1985 to 2014 and assume no adaptation measures.

Bentley-McKune also warned about El Niño: “Moreover, an exceptionally strong El Niño is currently forecast to still be in place when the 2027 pre-monsoon season begins, so the coming season could bring another period of extreme heat to South and Southeast Asia. Our findings show that extreme heat can lead to more preterm births, which have severe health risks. Heat protection needs to be in place before it arrives to protect mothers and babies.”

“The countries analysed have contributed relatively little to the historical emissions driving climate change, yet are disproportionately affected by climate-driven extreme weather compared with high-income, high-emitting countries, which also have more resources to adapt,” she said.

“Our estimates can help identify where greater health service capacity is needed, and adaptation measures – such as better antenatal care and early warning systems – should be prioritised. However, these could prevent only some of the preterm birth burden imposed by climate change, so limiting further warming remains crucial,” Bentley-McKune said.

Dr. Rashmi Agarwalla reviewed the briefing. She is the nodal officer for climate change and an associate professor in the Department of Community and Family Medicine at AIIMS Guwahati. She said: “Climate change is a public health emergency, and pregnant women and their babies are on the frontline, particularly in highly climate-vulnerable countries such as India, Bangladesh and the Philippines.”

“As a doctor working in India, emerging evidence suggests that extreme heat disproportionately affects pregnant women and newborns. Anemia, poor nutrition, and prolonged outdoor work further compound these risks, particularly in vulnerable communities. Yet, heat remains an often-overlooked threat to maternal and neonatal health within our healthcare systems,” Agarwalla said.

The release said the analysis should remind governments that, as temperatures rise, protecting mothers from heat must become a routine part of health-system preparedness, prenatal care, and community maternal health services.

It also urged governments to phase out fossil fuels and to increase international climate finance for developing countries, which would fund both adaptation and emission-reduction measures.