Maternal Smoking Linked to Severe Bronchiolitis in Infants

Blog Post created by Thomas3.20.2010 on Aug 14, 2012

Maternal smoking during pregnancy is one of several independent risk factors for infants developing severe bronchiolitis that requires mechanical breathing assistance at a hospital, according to a studypublished online August 6 in Pediatrics.

Jonathan M. Mansbach, MD, from the Department of Medicine, Children's Hospital, and Harvard Medical School, Boston, Massachusetts, and colleagues conducted a 3-year, multicenter (up to 16 centers) prospective cohort study of 2207 children younger than 2 years who presented with severe bronchiolitis during the months of November through March, beginning in 2007.

Of the 2207 children, 379 (17%) were enrolled in the intensive care unit, and 161 (42%) of those children required continuous positive airway pressure (CPAP) and/or intubation. Fifty-nine (37%) required CPAP, 64 (40%) required intubation, and 38 (23%) required both.

Of all the 2207 children, most (59%) were boys, 61% were white, most had a birth weight of less than 7 pounds, and the median age was 4 months (interquartile range, 2 - 9 months). Most of the children were breast-fed, had no parental history of asthma, and were born at term. The median hospital stay was 2 days, and the pathogens most often detected were respiratory cyncytial virus-A (RSV-A) (43%), RSV-B (30%), and human rhinovirus (26%).


In addition to collecting clinical information, the investigators conducted interviews to obtain patient demographics, medical and environmental histories, and symptom and acute illness details. Among the interview questions was, "Did the mother of [child] smoke cigarettes during the pregnancy?"

The researchers used multiple modelling and analysis methods to determine which children were more likely to need CPAP and/or intubation, controlling for 10 demographic and clinical factors including age, birth weight, maternal smoking, and time preceding emergency visits.

"[W]e found several factors independently associated with a child's need for CPAP and/or intubation: young age, low birth weight, child of mother who smoked during pregnancy, onset of respiratory symptoms <1 day before presentation, presence of apnea, severe retractions, room air oxygen saturation <85%, and inadequate oral intake," the researchers write.

For instance, of the 161 children who required CPAP and/or intubation, 46% were younger than 2 months (P < .001), 73% were born between October and March (P = .002), 16% weighed less than 5 pounds at birth (P = .01), and 19% had mothers who smoked during the pregnancy (P = .12).

In comparison, 28% of the total study population was younger than 2 months, 61% were born between October and March, 13% weighed less than 5 pounds at birth, and 15% had mothers who smoked during pregnancy.


In a multivariable model, the strongest predictors for requiring CPAP or intubation were age under 2 months (odds ratio [OR], 4.29-fold; 95% confidence interval [CI], 1.66 - 11.53), maternal smoking (OR, 1.38; 95% CI, 1.05 - 1.91), sleep apnea (OR, 4.78; 95% CI, 2.57 - 8.50), severe retractions (OR, 11.14; 95% CI, 2.40 - 33.19), room oxygen saturation lower than 85% (OR, 3.28; 95% CI, 2.02 - 4.82), and inadequate oral intake (OR, 2.47; 95% CI, 1.34 - 5.07).

Previous research has shown that mothers who smoke during pregnancy have children with impaired lung capacity at birth and into childhood. This new study, however, is the first study to find that smoking during pregnancy is an independent risk factor for "bronchiolitis requiring CPAP and/or intubation even after controlling for 9 other factors."

Limitations of the study include the inclusion of patients only from academic medical centers, which may limit generalizability of the results, plus variations in institutional care and use of resources. Strengths include the broadening of previous research into a multiyear and multicenter effort.

The researchers conclude, "The present data not only build on and extend previous findings about the respiratory ramifications of in utero smoke exposure for infants, but they also emphasize the need for continued work on smoking cessation."