By The Daily Climate

Women pregnant during heat waves face a higher risk of giving birth to babies with a rare defect causing blindness, according to new research.

The study, surveying 15 years of birth defect records in New York state, offers troubling implications for a warmer climate.

In the first study to explore a link between extreme heat and birth defects, researchers from the New York Department of Health and The State University of New York at Albany found that even a five-degree increase in temperature during crucial developmental stages in pregnancy increased the odds of an infant developing congenital cataracts.

The cataracts interfere with vision development in babies and are a leading cause of preventable blindness and vision impairment in children. The defect occurs in three of 10,000 births.

Permanent vision loss

Prompt and successful treatment – surgery to remove the cataract, then glasses or contacts to correct the vision – usually leaves few to no developmental effects, according to Linda Lindeke, an associate professor at the University of Minnesota's School of Nursing and Department of Pediatrics.

Failure to treat the affliction can cause a rewiring of connections to the brain, leading to permanent visual loss even if the cataract is later removed.

The study was published in the journal Environmental Health Perspectives in October. The researchers found no other significant links to other birth defects.

The study analyzed live birth records from upstate New York – the state minus New York City – from 1992 to 2006. Of those records, 65,750 infants were in utero in the summer during the critical phase when the eye is developed, between weeks four and seven in the pregnancy.

Among those 65,000 children, 6,422 were born with cataracts. Researchers found that a five-degree increase in the daily minimum apparent temperature – a formula derived using temperature, vapor pressure and wind speed – increased the likelihood of developing cataracts by 51 percent.

Few studies

"Although it is biologically plausible that extreme ambient outdoor temperatures during pregnancy could raise maternal core temperatures and cause birth defects," the researchers wrote, "few studies have assessed the relationship between high environmental temperatures and birth defects."

Indeed, heat exposure during pregnancy hasn't previously been linked to birth defects: Earlier studies looking at hot tub and sauna use, as well as cooking in a hot kitchen, lack of air conditioning or even exposure to temperatures above 100º Fahrenheit while pregnant have failed to find links to congenital defects.

But with temperatures expected to increase and extreme weather more common with climate change, the researchers, led by Alissa R. Van Zutphen of the New York State Department of Environmental and Occupational Epidemiology, suspect the risk of birth defects will rise.

"We found positive and consistent associations with congenital cataracts of multiple ambient heat exposure indicators," concluded Van Zutphen and her colleagues. "The potential for maternal hyperthermia to cause congenital cataracts, a leading cause of avoidable blindness and visual impairment in children, should be more closely examined."

This story was originally written for The Daily Climate and was republished with permission here. is an independent, foundation-funded news service covering climate change.

Extreme heat contributes to rare childhood blindness
Women pregnant during heat waves face a higher risk of giving birth to babies with a rare defect causing blindness, according to new research.