Researchers still don't know why some babies develop the obstruction, known as hypertrophic pyloric stenosis, said the study's lead author, Dr. Jarod McAteer, a surgery research fellow at Seattle Children's Hospital. This study just pinpoints some of the factors that increase the risk, he added.
What scientists do know is that in certain infants, the one-way valve, or sphincter, that allows partially digested food to progress from the stomach to the small intestine can stop working when the muscle that controls the valve's opening and closing gets too thick. At that point, the connection between the stomach and the small intestine is essentially blocked.
Babies are at risk only when they are between 3- and 6-weeks- old, McAteer said.
"Usually in the first couple of weeks of life, they are completely normal, healthy babies," he said. "Then they start vomiting and it progressively gets worse over a period of several days until they can't hold anything down."
The only solution is surgery to cut the muscle so it will relax and allow food to pass, McAteer said.
For the new study, McAteer and his colleagues from the University of Washington compared 714 infants who developed hypertrophic pyloric stenosis to 7,140 "control" babies who did not develop the obstruction.
After accounting for other known risk factors for obstruction, such as being male and first born, the researchers determined that bottle feeding also significantly raised the risk. In fact, bottle feeding was twice as common among babies with an obstruction, at 19.5 percent, compared with those in the control group (9.1 percent).
Babies with older mothers were also more likely to develop HPS.
Image: Baby with bottle, via Shutterstock