A study published today suggests that exposure to high levels of humid heat during pregnancy is associated with an increased likelihood of preterm birth. The research also indicates that low-dose aspirin taken during pregnancy may reduce this risk. Pregnant women are advised to consult a doctor before taking aspirin or other medications.
What Is Preterm Birth?
Preterm birth is defined as a live birth before 37 weeks of pregnancy. Globally, about 10% of babies (approximately 13 million) are born preterm each year. Approximately one million of these infants do not survive, making preterm birth the leading cause of death in children under five.
Types of preterm birth:
- Extremely preterm: before 28 weeks
- Very preterm: between 28 and 32 weeks
- Moderate to late preterm: between 32 and 37 weeks
Causes
The exact cause of preterm birth is often unknown. Many cases occur spontaneously. Factors that may increase risk include:
- Genetics
- Infections
- Chronic conditions such as diabetes and high blood pressure
- Exposure to environmental pollutants (e.g., bushfire smoke, pesticides)
- Extreme heat
These factors can contribute to inflammation, which is believed to increase preterm birth risk.
Humidity and Preterm Birth
Extreme heat can increase shock proteins in the blood, triggering inflammation, and may reduce blood flow to the placenta. Humidity impairs the body's cooling ability through sweat evaporation, adding strain. This may contribute to higher preterm birth rates in regions affected by climate change, such as South Asia and sub-Saharan Africa.
Study Details
A new study examined humid heat exposure during pregnancy and preterm birth risk, as well as the potential protective effect of low-dose aspirin. The study was conducted in the Democratic Republic of Congo, Zambia, Kenya, Guatemala, Pakistan, and parts of India.
Over 11,500 pregnant women participated. Half received a daily low-dose aspirin (81 mg) from enrollment until 36 weeks of pregnancy; the other half received a placebo.
Key findings:
- Preterm birth rate was lower in the aspirin group (11.6%) compared to the placebo group (13.1%).
- Among women not taking aspirin, each 1°C increase in temperature was associated with a 5% increase in preterm birth risk.
- This pattern was not observed in women taking low-dose aspirin.
- Later pregnancy heat exposure was linked to higher preterm birth risk in the placebo group but not in the aspirin group.
Limitations
- Temperature data were generalized across cities and may not reflect individual exposure.
- Researchers could not determine specific reasons for preterm birth or differences between groups.
The study adds to evidence that heat and humidity may increase preterm birth risk and suggests low-dose aspirin may reduce that risk. Further research is needed to replicate findings.
Recommendation
Pregnant women concerned about preterm birth risk should consult a doctor before taking any medications.