NEW YORK, Oct 05 (Reuters Health) -- Babies who are longer at birth have a higher risk of developing asthma later in life, while babies with larger head circumferences at birth are more prone to develop allergies, report New Zealand researchers.
On the other hand, babies that weigh less than 3.0 kilograms (about 7 pounds) at birth have only one-fifth the chance of developing asthma than heavier babies.
"These results suggest that increased fetal growth is related to an increased risk of asthma and (allergy) in childhood," write Dr. Philip Leadbitter from the Wellington School of Medicine in Wellington, New Zealand, and colleagues in the October issue of the journal Thorax.
The investigators measured the birth weight, birth length, and birth head circumference of 734 babies and tested them for evidence of asthma or tendency to allergy (atopy) once they reached the age of 11 to 13 years.
Babies with birth lengths greater than 56 centimeters (22 inches) were 6.4 times as likely to experience asthma symptoms before age 13 as babies who were shorter at birth, the results indicate. In contrast, babies with lower birth weights were far less likely to be diagnosed with or to experience symptoms of asthma compared with their heavier counterparts.
Infants with larger head circumferences (greater than 37 centimeters, or 14.5 inches) were more than three times as likely to have higher levels of IgE, a measure of allergic reactivity, than infants with smaller head circumferences, the researchers report. On the other hand, those with smaller head circumferences (less than 34 centimeters, or about 13 inches) were only half as likely to develop atopy, as shown by skin testing, as infants with larger head circumferences.
"Our findings suggest that smaller infants are at reduced risk of developing asthma and that, as the size of the infant at birth increases, so does their risk for subsequently developing asthma and atopy," the investigators conclude.
"The reasons for the association between increased fetal growth and the subsequent risk of asthma and atopy are unclear and were not addressed in this study," the authors note. Nevertheless, they speculate that "relative undernutrition may be protective while overnutrition increases the risk for asthma and atopy in later childhood."
