When the heat rises, so does the risk

Millions of pregnant women across India's informal workforce keep working straight through the hottest months, often with no paid leave to fall back on. Drag the slider below to feel out what the research found.

Wet Bulb Globe Temperature (WBGT) Caution
22°C27°C32°C37°C42°C
WBGT zones follow ACGIH Threshold Limit Values for continuous heavy manual work (ACGIH, 2017) — a widely used international reference, not part of the original brief. Risk commentary above 30°C reflects the Tamil Nadu findings below.

Pregnancy already asks a lot of the body. Heat asks for more — and takes away the body's usual way of coping.

As pregnancy progresses, the added metabolic load of carrying a child combines with a reduced ability to shed heat. For a woman doing manual outdoor or home-based work, that leaves very little room before dehydration and heat strain set in — and the clinical evidence below shows what's at stake when that margin runs out.

THE CLINICAL EVIDENCE

Timing matters

A retrospective study linking pregnancy registries to weather records across Nagpur and Belagavi found that when in pregnancy the heat exposure happens changes what it does. Tap a trimester.

TAMIL NADU COHORT · 800 PREGNANT WORKERS

What high heat exposure meant for outcomes

Women doing moderate-to-heavy manual work were tracked through pregnancy. Almost half showed high occupational heat exposure — and for them, the risk of complications roughly doubled. Choose an outcome to see it laid out.

2.4× the odds
Each dot represents a share of outcomes among heat-exposed vs. lower-exposed women. Illustrative, based on the adjusted odds ratio — not a literal headcount.

FIVE INFORMAL SECTORS, TAMIL NADU

Whose workdays run hottest

88%

of 1,560 monitored outdoor workers across agriculture, construction, brick manufacturing, saltpan work, and stone quarrying were exposed to WBGT levels above recommended safety thresholds during summer months.

Heavier physical workload and the season itself were the strongest predictors of both productivity loss and heat-related symptoms. Tap a sector to see it.

BEYOND PREGNANCY

A risk that rarely makes the statistics

Heat, kidneys, and a quiet data gap

+
Surgical team in an operating theatre

Heat exposure has also been separately linked to acute kidney injury and chronic kidney disease of unclear origin among outdoor manual labourers — worsened by dehydration, dust, and physical exertion. This kind of harm builds slowly and can be irreversible, so it rarely shows up in short-term heat wave death tolls, even though the toll is real.

Researchers reviewing the global literature found that studies — especially in South Asia — still focus mostly on mild, short-term symptoms rather than the long-term cardiovascular, neurological, and organ damage heat can quietly cause. Earlier work pointed to the same gap: under-recording of occupational heat illness, limited workplace research, and employers reluctant to publish findings that might look bad for industry reputation.

THE HIP-INDIA COHORT

Three climates, one open question

Even with growing evidence, researchers say we still don't fully understand the mechanisms and safe thresholds for outdoor and informally employed pregnant women in Indian settings. The ongoing Heat in Pregnancy–India study is measuring heat, humidity and air pollution exposure — plus physiological heat strain — across three very different climates.

WHERE THIS POINTS CLINICALLY Community health worker speaking with a group of women

Pregnant informal workers are rarely tracked by workplace heat-monitoring, and rarely followed closely through antenatal care during extreme heat either. That's the gap.

One practical response researchers have proposed: build heat-risk screening into routine antenatal care itself, delivered through ASHA and Anganwadi frontline worker networks and public antenatal clinics — channels that already have trusted, established contact with pregnant women in a way street-level or worksite outreach can't match. Findings from cohorts like HiP-India aim to eventually define India-specific heat thresholds and clinical protocols that could be built into that training.

References
  1. John, P., & Jha, V. (2023). Heat stress: A hazardous occupational risk for vulnerable workers. Kidney International Reports, 8(7), 1283–1286. doi.org/10.1016/j.ekir.2023.05.024
  2. N, S. V. S. C., & Xu, Z. (2024). Heat and health of occupational workers: a short summary of literature. Journal of Occupational Health, 66(1). doi.org/10.1093/joccuh/uiae018
  3. Rekha, S., Nalini, S. J., Bhuvana, S., Kanmani, S., Hirst, J. E., & Venugopal, V. (2023). Heat stress and adverse pregnancy outcome: Prospective cohort study. BJOG, 131(5), 612–622. doi.org/10.1111/1471-0528.17680
  4. Shankar, K., et al. (2023). Associations between ambient temperature and pregnancy outcomes from three South Asian sites of the Global Network Maternal Newborn Health Registry. BJOG, 130(S3), 124–133. doi.org/10.1111/1471-0528.17616
  5. Srinivasan, K., Maruthy, K., Venugopal, V., & Ramaswamy, P. (2016). Research in occupational heat stress in India: Challenges and opportunities. Indian Journal of Occupational and Environmental Medicine, 20(2), 73. pmc.ncbi.nlm.nih.gov/articles/PMC5299815
  6. Thiruvengadam, R., et al. (2025). Cohort profile for the Heat in Pregnancy-India (HiP-India) study. Wellcome Open Research, 10, 472. doi.org/10.12688/wellcomeopenres.24393.2
  7. Venugopal, V., Latha, P. K., & Shanmugam, R. (2026). Quantifying the impact of heat stress on labour productivity in outdoor workplaces in Southern India amid a changing climate. Scientific Reports, 16(1). doi.org/10.1038/s41598-026-41807-6

Added for context (not part of the original brief): American Conference of Governmental Industrial Hygienists (ACGIH). (2017). Heat Stress and Strain: TLV Physical Agents, 7th Edition Documentation. Used here to give the interactive temperature gauge real-world WBGT reference points. See OSHA's Technical Manual, Section III Chapter 4, which summarizes the ACGIH TLV/Action Limit framework.