Each summer, obstetric units across Delhi see a familiar and concerning shift. Preterm presentations increase, cases of fetal growth restriction become more frequent, and hypertensive complications arise
at gestational ages where they ought not to. Summers are growing longer and more severe, and the clinical picture is responding accordingly. What remains insufficiently understood outside specialist circles is the direct role that extreme heat plays in driving these outcomes.
Pregnancy places the body under sustained physiological demand. Blood volume increases by approximately 40 to 50 percent, cardiac output rises, and the kidneys, liver, and lungs all function under greater load than in the non-pregnant state. When ambient temperatures exceed 45°C, the body’s thermoregulatory mechanisms must compete with the circulatory and metabolic demands of pregnancy itself. Under prolonged or intense heat stress, that competition carries real risk for both mother and child.
Dr Renu Malik, Gynaecologist and Obstetrician, Director, Malik Radix Healthcare, shares all you need to know:
What the Research Tells Us
The clinical concern around heat and pregnancy is well supported in the literature. Research published in Nature Climate Change and The Lancet Planetary Health has shown that heat exposure at any stage of pregnancy is associated with increased rates of preterm birth, low birth weight, and stillbirth. A study drawing on data from over 57 million births in the United States identified a clear relationship between rising temperatures and early delivery. Consistent findings have been reported across research conducted in South Asia and sub-Saharan Africa, in populations and climates directly relevant to the Indian context.
Importantly, prolonged exposure is not a prerequisite for harm. Studies indicate that even a single day of temperatures significantly above regional seasonal norms can elevate complication risk, with the degree of risk increasing with both the intensity and duration of exposure. For a city that now routinely records temperatures between 44°C and 46°C across several consecutive weeks between April and June, this has substantial public health implications. There is also emerging, though still preliminary, evidence that heat exposure during the first trimester may be associated with certain congenital anomalies.
Preterm Labour: Heat as a Trigger
The association between heatwave conditions and preterm labour is among the more consistent findings in this area of obstetric research and one that remains underrecognised in clinical practice in India. Presentations of preterm contractions with no identifiable risk factors, upon closer history-taking, frequently reveal periods of significant dehydration during episodes of extreme heat.
The underlying mechanisms are well established. Dehydration reduces plasma volume, diminishing uterine perfusion and stimulating the release of oxytocin and prostaglandins, both of which are implicated in the initiation of labour. Additionally, heat stress activates systemic inflammatory pathways that can precipitate premature cervical ripening, independent of hydration status, further increasing the risk of early delivery.
Low Birth Weight and Placental Stress
The placenta is acutely sensitive to the circulatory changes induced by heat stress. When a mother is dehydrated, blood flow is redirected toward the skin to regulate body temperature, and the placenta receives less than it requires. Over time, a reduced supply of oxygen and nutrients to the fetus results in slower growth and low birth weight.
The consequences of low birth weight extend well beyond the neonatal period, with documented associations with metabolic syndrome and cardiovascular disease later in life. Heat stress has also been linked to hypertensive disorders of pregnancy, including preeclampsia, which remains a leading cause of maternal mortality globally and is observed with increased frequency across North Indian tertiary centres during the summer months.
Who Is Most at Risk
The highest-risk groups are broadly predictable. Women in outdoor occupations, those without access to mechanically cooled environments at home, and those in the third trimester, when physiological reserve is at its lowest face the greatest combined burden.
In Delhi, where electricity supply is frequently disrupted during peak summer demand and residential housing in many areas retains heat through the night, these are not hypothetical vulnerabilities. Women with gestational diabetes, anaemia, or multiple pregnancies, as well as those at the extremes of reproductive age, carry an additional layer of clinical risk that is compounded by heat exposure.
Clinical Guidance and Shared Responsibility
The preventive measures are well within reach, provided awareness exists and support is in place. Adequate hydration throughout the day, beginning well before thirst develops is the single most effective protective measure available. Avoidance of outdoor exposure between 11 am and 4 pm, wearing light, breathable clothing, access to ventilated rest areas, and reduced physical exertion in the later months of pregnancy all provide meaningful clinical benefit.
Responsibility does not rest with the pregnant woman alone. Employers are obligated to provide reasonable accommodation during periods of extreme heat, and families must ensure that basic needs such as drinking water, adequate rest, and access to cooling are consistently met.
Any warning signs including decreased fetal movements, persistent contractions, dizziness, or reduced urine output must prompt immediate medical evaluation. In conditions where ambient temperatures remain above 40°C for extended periods, the interval between a warning sign and a serious maternal or fetal complication can be considerably shorter than anticipated.
