Summer heat may affect baby's birthweight

Anyone who has been in the last stages of pregnancy during hot summer months knows that the heat can sap an expectant mother’s energy and swell her feet. Surprisingly, the outside temperature also affects the baby in her womb, according to a recently published study by Israeli and American researchers.

The study showed that air temperature was associated with decreased birth weight as well as the earlier onset of labor.

“For example, an increase of 8.5 degrees Celsius in the last trimester of average exposure was associated with a 17-gram [six-ounce] decrease in birthweight,” said Ben-Gurion University of the Negev Prof. Itai Kloog of the department of geography and environmental development.

“We also found that exposure to high air temperature during pregnancy can cause preterm birth,” said Kloog, whose previous published studies looked at the detrimental effect of air pollution on pregnant mothers and their newborns; and how artificial light at night may increase the risk of breast cancer.

The evaluation of temperature and birth outcomes was carried out between 2000 and 2008 in Massachusetts. Kloog collaborated with colleagues from the School of Public Health at Harvard University — Steven J. Melly, Prof. Brent A. Coull, Francesco Nordio and Prof. Joel D. Schwartz.

To do this, the scientists developed a novel high-resolution air temperature estimation model to predict daily air temperature within one kilometer. They then estimated address-level exposure to air temperature during various prenatal exposure periods from conception through birth for each mother involved in the study.

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