Researchers at Seoul National University Hospital (SNUH)’s Environmental Health Center have found that exposure to ozone during pregnancy increases the risk of developing congenital malformations.

The center analyzed 150,000 congenital malformations between the ages of 0 and six born between 2008 and 2013 to find out whether exposure to ozone increased the risk of congenital disabilities.

According to National Health Insurance Service claims, the most common anomalies that the 150,000 children had were the circulatory system (24.6 percent), including the heart, followed by musculoskeletal (22 percent) and urinary (13.3 percent). Eyes, ears, face, and neck showed the lowest defection rate with 5.3 percent.

Also, congenital anomalies related to postnatal endocrine and metabolic diseases appeared in the order of metabolic disorders (22 percent), endocrine system (6.6 percent) and hypothyroidism (6 percent) in children under the age of six.

Regarding ozone’s effect on deformity, the impact varied depending on the pregnancy period.

During the middle of pregnancy (four to seven months), the possibility of congenital heart disease increased by 5 percent, while problems in the musculoskeletal and urinary system increased by 7.1, and 11.7 percent, respectively, every time the atmospheric ozone concentration increased by about 0.018 ppm.

For late pregnancy (eight to 10 months) congenital heart and musculoskeletal disorders increased by disease 4.2 and 3.6 percent, respectively.

Ozone also has adverse effects on postnatal endocrine and metabolic diseases.

During the middle of pregnancy, congenital anomalies related to metabolic diseases increased by 11.7 percent, while hypothyroidism increased to 9.7 percent every time the atmospheric ozone concentration increased by about 0.018 ppm. For late pregnancy, congenital anomalies related to metabolic diseases increased by 8.2 percent.

“This study has once again confirmed the importance of clean air quality, including ozone, inhaled and exposed during pregnancy,” the research team said. “Especially, exposure to mid-trimester ozone has been shown to increase the risk of congenital anomalies.”

SNUH Environmental Health Center director Hong Yoon-chul also said, “When exposed to air pollutants such as ozone and fine dust, the incidence of miscarriage and premature infants can be increased due to oxidative stress. Because of the increased risk of congenital anomalies, we advise pregnant women to refrain from outdoor activities when air pollution is severe.”

Causes of congenital anomalies are complex, but precautionary efforts and prenatal testing can prevent some of the deformities, he added.

International Society for Environmental Epidemiology published the result of the study.