“Hot temperatures will create a dangerous situation in which heat illnesses are likely,” the message read, advising all San Franciscans to drink plenty of fluids, seek out air-conditioning, and check up on relatives and neighbors. The advisory also warned of heat-related illnesses—particularly for the elderly, children, and sick people—as well as pets and livestock.
Some scientists think another group should be added to the list: pregnant women.
A handful of researchers in the United States, Canada, and elsewhere are methodically accumulating evidence suggesting that higher temperatures could be linked to a higher risk of premature births, stillbirths, or other negative pregnancy outcomes. The findings in each case, while compelling, still raise as many questions as they seem to answer, and all the researchers say that much more work needs to be done. But they also suggest that enough evidence has already surfaced to warrant increased scrutiny—particularly as global warming is expected to drive average temperatures ever upward over coming decades.
A decade ago, Basu noticed something odd in the scientific literature documenting the health risks of air pollution—a much clearer and well-established relationship. She knew that past research, including some of her own, had shown a link between air pollution and negative pregnancy outcomes, but while the literature alluded to a seasonal pattern, none of the studies controlled for temperature. “I said that some of this must be due to temperature,” Basu recalled, “but we don’t have any data to support that.”