Researchers found that infants of mothers who smoked were 50 per cent more likely to be admitted to a hospital or die from any of a wide variety of infectious diseases than babies of mothers who did not smoke.
For the study, researchers reviewed hospitalisation records and death certificates of 50,000 infants born in the state of Washington between 1987 and 2004.
The case-control study assessed infant hospitalisations and deaths due to respiratory and non-respiratory infectious disease.
"We've known for a long time that babies born to mothers who smoke during pregnancy are at high risk for serious medical problems relating to low birth weight, premature delivery and poor lung development," said Abigail Halperin, lead author of the study published in journal Pediatric Infectious Diseases.
"While respiratory infections have been recognised as a common cause of these sometimes life-threatening illnesses, this study shows that babies exposed to smoke in utero also have increased risk for hospitalisation and death from a much
broader range of infections, both respiratory and non-respiratory, than we knew before," Halperin said.
The findings were largely independent of birth weight and gestational age, "thus even full-term babies with normal weight are at increased risk for hospitalisation or death from multiple types of infections if their mother smoked," she said.
The results suggest that exposure to smoke during pregnancy harms infants' immune responses more generally, not just within the respiratory system, she said.
The study also found that when mothers cut back on their cigarette smoking or quit part way through their pregnancy, it seems to lower their child's risk of infection.
The study will be presented this week at the American Academy of Pediatrics (AAP) National Conference and Exhibition in Orlando.