"We have a pattern where the prevalence is very much highest among young women and it's growing more rapidly among that group than any other group," said Russell Kirby, a professor at the University of South Florida and the lead author of the study.
Kirby's study could not explain why the birth defect is becoming more common, and gastroschisis itself is not well understood.
The malformation involves an opening next to the belly button, through which the baby's intestines protrude.
Newborns with gastroschisis require immediate surgery to close the hole and put the organs back in place.
Most babies with gastroschisis survive, but Kirby said some children have problems with growth and development and there is not a lot of research about the long term outcomes for these kids.
By general estimates, the condition is relatively rare, with a rate of 2 to 3 cases per 10,000 live births in the U.S. But in recent years, studies have suggested the defect is being seen more often....
....The increase in gastroschisis primarily affected mothers under age 25, and especially under age 20, whereas those who gave birth in their 30s had no change in their risk of having a baby with the birth defect.
Mothers who had their babies in their early twenties experienced a 5.8 percent increase each year in the risk of having a child born with gastroschisis, Kirby's group reported in the medical journal Obstetrics & Gynecology.
Among these mothers, the number of babies born with gastroschisis went from 4 out of every 10,000 babies in 1995 to 7 in 10,000 babies in 2005.
Teen mothers saw a 6.8 percent yearly increase in the proportion of babies born with gastroschisis.