Teen girls who become pregnant after gastric bypass surgery may have an increased risk of having children with birth defects, researchers said today.

However the conclusion is based on a small number of cases, and some researchers are skeptical of the link.

The surgery, which staples the stomach and rearranges the gut anatomy, can lead to deficiencies in the way the body absorbs some vitamins and nutrients from food. This may affect the development of the brain and spinal cord in the growing fetus — the baby may be born paralyzed with so-called neural tube defects, such as spina bifida.

Deficiencies in the vitamin folic acid, or folate, are known to increase the risk of neural tube defects.

Although women of all ages who have gastric bypass surgery may be at risk for vitamin deficiencies, the surgery is particularly concerning for teens who become pregnant, because they may be less likely than older women to heed dietary advice, said study researcher Dr. Diana Farmer, a pediatric and fetal surgeon at the University of California, San Francisco.

"Adolescents are known to have poor compliance, so they don’t do what they're told, with taking medication and doing what their parents say," Farmer said. "And therefore they may not take their right prenatal vitamins, their right supplementation."

The number of teens getting this surgery has more than doubled over the last two or three years, she said.

Farmer and her colleagues documented a case of a young female patient who came to the Fetal Treatment Center at UCSF because her fetus had spina bifida. The patient had undergone gastric bypass surgery as an adolescent. The researchers also reviewed six additional cases of mothers who had received gastric bypass surgery in adolescence and later had children born with neural tube defects.

"If [teens] are going to do this operation, they have to be very carefully monitored and advised about this risk," Farmer told MyHealthNewsDaily.

However, not all researchers agree that the surgery poses a significant risk of folic acid deficiencies.

"We have treated well over 100 teens and have followed them over the years, and have not appreciated any issue with low folate level after gastric bypass," said Dr. Thomas Inge, a pediatric surgeon at Cincinnati Children's Hospital Medical Center and director of the Surgical Weight Loss Program for Teens. "Our diet in the U.S. is basically laced with folate, and the incidence of fetal anomalies due to folate deficiency has dropped since this public health measure went into effect," he told MyHealthNewsDaily.

He also said obesity itself poses problems during pregnancy, and most scientific evidence "indicates that pregnancy is safer, not more hazardous, after gastric bypass."

Farmer's study will be presented today (Oct. 3) at the American Academy of Pediatrics (AAP) National Conference and Exhibition in San Francisco. Inge, who commented on the work before attending the presentation, said he was interested to see what data the researchers had to support their concerns.

 This article was provided by MyHealthNewsDaily, a sister site to LiveScience.