Key Takeaways
- A study of 46,773 deliveries across four Pakistani cities found limited evidence linking extreme heat to premature births.
- Initial analysis suggested a higher risk but adjustments for city differences reduced the link to statistical insignificance.
- Researchers recommend better data collection and more rigorous analytical methods.
A recent study examining the impact of extreme heat on pregnancy outcomes in Pakistan has found that while initial findings indicated a potential connection, further analysis revealed limited evidence. The research, led by Dr. Shaper Mirza from Lahore University of Management Sciences (LUMS) and Dr. Faridah Amir Ali from the Indus Hospital and Health Network, analyzed 46,773 deliveries across Karachi, Lahore, Muzaffargarh, and Badin between June 2021 and July 2024.
The study initially suggested that women exposed to at least one hot and humid day above 33°C during the final trimester had a 33% higher risk of giving birth prematurely. However, after accounting for differences between cities and seasonal birth patterns, this apparent connection almost disappeared. The adjusted analysis linked heat exposure to just a 0.06% difference in premature births, which was statistically insignificant.
Dr. Mirza explained that Badin, one of the study’s locations, played a significant role in the initial results. Nearly 96% of births in Badin were preceded by at least one hot and humid day above 33°C, with the city also having the highest premature birth rate, ranging from 27.6% in November to 46.9% in August.
The researchers noted that Badin’s seasonal pattern could be linked to hospital referrals related to the agricultural calendar, seasonal infections, and changes in maternal nutrition. This suggested that a basic analysis might confuse living conditions with heat exposure effects.
To test the heat effect more closely, the team used five different analytical methods on the full dataset, the dataset without Badin, and Badin’s data separately. Two methods found no link between heat and premature birth, while two others found a connection only when Badin was included. The relationship disappeared or reversed when the city was removed.
Only one method produced a consistent result, finding that women exposed to more days of 40°C or above during the middle months of pregnancy had around 4% higher odds of premature delivery. However, Dr. Mirza emphasized that this finding was weak and could be due to an unmeasured factor affecting both heat exposure and premature birth by as little as 5%. An advanced model examining delayed heat effects also found no lasting impact on premature birth.
The researchers concluded that future studies must carefully account for location and seasonal differences before linking extreme heat to premature birth. They recommended using multiple analytical methods and collecting more detailed information about mothers’ health, circumstances, and actual heat exposure.
Dr. Amir Ali stated, 'Our findings suggest that while extreme heat may play a role in some cases, it is not the sole factor influencing premature births.' She added, 'Further research with better data collection will be crucial to understanding this complex issue more comprehensively.'
Our findings suggest that while extreme heat may play a role in some cases, it is not the sole factor influencing premature births.
Dr. Faridah Amir Ali, Indus Hospital and Health Network
