Young women who have both a sexually transmitted disease and a urinary tract infection just before or early in their pregnancy are four times more likely to have a baby born with intestines and other organs outside the abdomen, according to a study by University of Utah researchers.

It is published in the online British Medical Journal.

The condition, called gastroschisis, is most common in babies whose mothers are under age 20, occurring at a rate of 1 in 575 births. Among women of all ages, it occurs in 1 in 2,272 births.

And likelihood drops as maternal age climbs, according to Marcia Feldkamp, Ph.D., physician assistant and assistant professor of pediatrics at the U. School of Medicine. She directs the Utah Birth Defect Network, which teamed up with the National Center on Birth Defects and Developmental Disabilities and the Utah Department of Health for the project as part of the National Birth Defects Prevention Study. The NBDPS uses birth defect surveillance systems in Utah and nine other states.

It's a preliminary finding regarding a mysterious birth defect that appears to be increasing worldwide, including in Utah, she said. In most cases, the small and sometimes large intestines are outside the abdomen. Sometimes all or part of the stomach is, too. More rarely, ovaries, fallopian tube or testes are. It's just slightly more common in boy babies.

In 90 percent of cases, the baby survives after surgery to place the organs, which are normally formed, where they belong.

"We don't now how it occurs or the timing, which makes it difficult to study," Feldkamp said. But given a previously shown strong link to young maternal age, researchers decided to look at what put that age group at much higher risk. Moms under 20 are 11 times more likely to give birth to a baby with gastroschisis than those over 25.

"Everyone's assumed it must be something environmental. Are these young moms taking on risky behaviors other women are not taking on?"

Researchers looked at infection because of their increase in tandem with the rising incidence of the birth defect. In Utah, for instance, an unrelated study found a tenfold increase in gastroschisis from 1971-2002, Feldkamp said. And sexually transmitted diseases, particularly chlamydia, are a growing problem, particularly among female teens.

They compared data on mothers of 505 babies with gastroschisis and a control group of 4,924 babies without the birth defect in the 10 states.

"We found that women who reported both urinary tract infection and STD one month prior to conception through the first trimester were far more likely" to have babies with gastroschisis, which occurs in the first trimester.

Feldkamp said the link may be even stronger, because they may be "missing women who have infection who we are calling unexposed." That's particularly true of chlamydia, a common STD that often has no symptoms and so goes undiagnosed. It was the most commonly identified STD in the study, she said.

More study is needed to verify the finding, and there's much more researchers would like to learn, she said. If they can find funding, they'd like to to collect blood and other biologic samples when the defect is identified prenatally, which typically occurs between 18 and 20 weeks, "to get a better handle on exposures, as opposed to self-report."