Gastroschisis — a rare birth defect in which a child is born with his or her organs outside the body — has become worryingly more common in recent years, particularly for young African American mothers, according to the Centers for Disease Control and Prevention.

In a new report this month, the public health agency said that it found 30 percent more cases of the disease between 2006 and 2012 than it did from 1995 to 2005, the Washington Post reports.

Among African American mothers who were younger than 20, the number of babies born with the disease jumped 263 percent.

“It concerns us that we don’t know why more babies are being born with this serious birth defect. Public health research is urgently needed to figure out the cause and why certain women are at higher risk of having a baby born with gastroschisis,” said Coleen Boyle, the director of CDC’s National Center on Birth Defects and Developmental Disabilities, in a statement.

Overall, about 2,000 U.S. babies are born each year with gastroschisis, according to the CDC report.

No one knows what causes infants to be born with their intestines and other visceral organs — the stomach, the liver — protruding through a small hole near their belly button or why the rate is increasing.