Understanding the effects of extreme heat in pregnancy, the HiP-India project

Background

Pregnant women, particularly those in low- and middle-income countries, are among the most vulnerable populations to climate change. India has experienced a marked rise in the intensity, frequency, and duration of heatwaves over the last half-century, with 2022 and 2024 being the hottest years since 1901.

Extreme heat exposure has been linked to several adverse pregnancy outcomes, including:

• Preterm birth
• Stillbirth
• Gestational diabetes
• Small for gestational age babies
• Preeclampsia

However, the biological mechanisms linking environmental heat to these outcomes remain poorly understood.

Aim

The Heat in Pregnancy – India (HiP-India) project is a multi-partner coalition of researchers across India and the UK seeking to understand why exposure to extreme heat leads to adverse birth outcomes. This Wellcome Trust-awarded project is a collaborative effort between the Translational Health Science and Technology Institute (THSTI), Delhi, the Chhattisgarh Institute of Medical Sciences (CIMS), Imperial College London (ICL), the University of Oxford, The George Institute India, and the Pondicherry Institute of Medical Sciences (PIMS), which aims to identify the critical windows and mechanisms of heat-related risk during pregnancy and develop evidence-based strategies to protect pregnant women and babies from the impacts of rising global temperatures.

Research methodology

Who we are studying

600 women with singleton pregnancies were recruited between 11 and 14 weeks of gestation

Where

Three distinct climate zones across India:

• Gurugram, Delhi NCR - Semi-arid climate with extreme temperature variations
• Bilaspur, Chhattisgarh - Humid subtropical to tropical wet and dry climate
• Puducherry - Tropical wet and dry climate with persistently high temperatures

When

Participants were recruited during both warm season (March-July) and cool season (November-February) to capture varying heat exposures

I. Quantitative Study:

What we measure:

Environmental exposures

• 24-hour heat, humidity, and air pollution monitoring in homes and workplaces each trimester
• Personal heat exposure using wearable devices and validated monitoring equipment
• Perceived heat stress through modified questionnaires

Maternal indicators

• Physiological heat strain (i.e. urine specific gravity, core body temperature, heart rate, blood pressure)
• Hemodynamic parameters using non-invasive monitoring
• Blood samples to evaluate circulating biomarkers of placental function and stress

Fetal development

• Serial ultrasound assessments to evaluate growth and fetal-placental blood flow
• Cardiotocography in the third trimester to monitor fetal well-being
• Assessment of uterine and umbilical artery blood flow

Birth outcomes

• Delivery outcomes for both mothers and newborns
• Lactation physiology assessment in a subset of 100 women during the first two weeks after delivery

II. Policy Analysis:

A review of Heat Action Plans (HAPs) across India will be conducted to evaluate how well they address the needs of pregnant and lactating women, and to identify gaps and opportunities for gender- and maternal-health–sensitive adaptations.

III. Qualitative Study:

To augment the clinical and physiological evidence, the study also examines how women, families, and communities adapt to extreme heat in their daily lives and how health systems and policies can better support them.

What we measure:

• Document women’s lived experiences of heat stress during pregnancy and lactation in informal and underserved urban settings
• Identify community-led coping strategies and barriers to adaptation
• Work with women’s groups, health providers, and policymakers to co-design feasible, gender-sensitive solutions
• Provide evidence for national and local guidance to protect maternal and newborn health under climate change