Heat Waves May Put a Pregnancy at Risk

The rates of preterm birth increase after heatwaves, according to a new study. The findings underline the wide scope of risks caused by extreme weather conditions.

Heat waves are becoming more common in the United States: their frequency increased from an average of two per year during the 1960s to six per year during the 2010s and 2020s.

Extreme heat may worsen health risks from chronic conditions, such as cardiovascular, mental, respiratory, and diabetes-related diseases, as well as cause acute kidney injury. Moreover, more deaths occur during heat waves.

A new study published in JAMA Obstetrics and Gynecology examined the impact of heat waves on preterm and early-term births.

The analysis used birth records from 1993 to 2017 in the 50 largest U.S. metropolitan areas during the hottest months. Overall, the study included 53 million births, covering 52.8% of births in the U.S. over this period.

The heat wave was defined as four consecutive days of mean temperatures exceeding the local 97.5th percentile. The study found heat waves were more common in later years, reflecting the increasing temperatures due to climate change.

During the 25 years, there were 2.15 million preterm births and 5.8 million early births. After a heatwave, the rates of preterm births increased by 2% and early births by 1%.

Increases were more significant for heat waves of longer duration and higher temperatures. Populations associated with lower socioeconomic status were more affected.

Preterm birth is when a baby is born before 37 weeks of pregnancy has been completed. It is the leading cause of infant mortality and can lead to long-term health issues, including respiratory, cognitive, gastrointestinal, and behavioral. In the U.S., about 10.5% of all infants are born preterm.

Early-term infants, delivered at 37-38 weeks gestation, are also at a higher risk of long-term complications and an elevated risk of infant mortality. Nearly one-third of babies (28.8%) in the U.S. are born early term.

Protecting yourself from heat

Although pregnant women are among the most vulnerable to heat waves, extreme temperatures can be dangerous to anyone. The Federal Emergency Management Agency recommends following these precautions to protect yourself and others from heat:

  • Check the forecast for the excessive heat warning before making plans.
  • Never leave pets or people in a car on warm days. Infants and children are especially in danger of getting a heat stroke or dying.
  • Drink more fluids regardless of your activity level. Don’t wait until you’re thirsty to drink.
  • Find air conditioning if you don’t have one at home consider going to a shopping mall or public library.
  • When outside, wear loose, lightweight, light-colored clothes, as well as a wide-brimmed hat and sunglasses.
  • Wear sunscreen with a high SPF to protect your skin from the sun. Apply it 30 minutes before going outside during the day, and remember to reapply it every two hours.
  • Limit outdoor activities to morning and evening when the temperature is the lowest.
  • Eat light — avoid hot, heavy meals that add heat to the body.

As the frequency of heat waves is unlikely to decrease in the near future, it is crucial for both pregnant and non-pregnant individuals to take precautions against the heat.


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