A study of 90 pregnant women in Puerto Rico found that those who experienced severe nausea and vomiting were 10 times more likely to have the Helicobacter pylori bacterium in their stomachs than women who did not feel sick.
The two groups of women were matched for age and number of previous births and were all in the first three months of pregnancy.
"We found H pylori in 83% of the women with morning sickness, but only 7% of the controls were positive," said Dr Nilda Santiago, who conducted the study with colleagues at the Ponce School of Medicine in Puerto Rico.
The team now plan to test women who plan to become pregnant for H pylori and treat the infection before they conceive.
Antibiotics for ulcers
"If our theory is correct, the antibiotic treatment should eliminate morning sickness in most of these women," the medical school's associate professor, Dr Alvaro Reymunde told a meeting of the American College of Gastroenterology.
The majority of stomach ulcers are caused by the bacteria, which can be eliminated by a course of three antibiotics in combination.
Dr Nicky Jackson from the Institute of Obstetrics and Gynaecology at Queen Charlotte's Hospital in London said that if there was an easy treatment for morning sickness "it would make life an awful lot easier for many women".
But, she pointed out that, while some of the antibiotics used to treat H pylori are theoretically safe to use in pregnancy, doctors and women may be reluctant to use them.
"The problem is testing any drug in women in the early stages of pregnancy - you really have to weigh up the benefits," she said.