A new study examining nearly 47,000 births across four Pakistani cities has found that extreme heat during pregnancy has little to no significant connection with premature births, challenging assumptions drawn from earlier international research.
Read More: UN agencies say one in 10 babies born prematurely in 2022
The study, led by researchers Dr Shaper Mirza of the Lahore University of Management Sciences (LUMS) and Dr Faridah Amir Ali of the Indus Hospital and Health Network, analysed 46,773 births recorded between June 2021 and July 2024 in Karachi, Lahore, Muzaffargarh and Badin.
Premature birth, defined as delivery before 37 weeks of pregnancy, is the leading direct cause of newborn deaths worldwide. Pakistan has one of the highest rates of preterm births globally while also experiencing prolonged periods of extreme summer temperatures.
Researchers initially observed that mothers exposed to at least one hot and humid day exceeding 33°C during the final trimester appeared to have about 33% higher odds of premature delivery. However, after adjusting for differences between cities and seasonal birth patterns, the association almost disappeared, shrinking to a statistically insignificant 0.06 percentage-point difference.
The findings suggest that the earlier association was largely influenced by Badin, where nearly all pregnancies experienced extreme heat and where premature birth rates were consistently higher due to factors such as seasonal infections, nutrition and healthcare referral patterns rather than temperature alone.
To verify the results, researchers applied five separate analytical methods. Four found either no consistent relationship or results that disappeared after accounting for regional differences.
Only one method suggested that repeated exposure to temperatures of 40°C or above during the middle months of pregnancy was linked to a modest increase in the likelihood of premature birth, equivalent to roughly a 4% rise in risk. Even then, researchers described the finding as weak and potentially influenced by other unmeasured factors.
Read More: In Jacobabad, mothers bear brunt of climate change
The authors recommend future studies collect more detailed information on maternal health, living conditions and actual indoor heat exposure before drawing firm conclusions about heat-related pregnancy risks.