Male babies born to mothers with asthma have a significantly lower lung function, which may affect their lung function trajectory and risk of developing respiratory disease, Australian research shows.

The finding is based on analysis of lung function data from more than 600 babies measured at 5–6 weeks of age from two large birth cohorts from the Australian Breathing for Life Trial (BLT) and the Bern Infant Lung Development (BILD) cohort in Switzerland.

All 406 BLT infants were born to mothers with asthma in pregnancy, while 193 of the 213 (91%) BILD infants were born to mothers without asthma.

According to researchers led by Professor Joerg Mattes from the University of Newcastle, NSW, it’s the first time an association between maternal asthma and lung function parameters at 5–6 weeks of age has been investigated.

Writing in their paper published in Thorax researchers said the main outcome variable was an integrated measure of the entire respiratory system, including airflow limitation and control of breathing – tPTEF:tE% (time to reach peak tidal expiratory flow as a percentage of total expiratory time),

A statistical interaction between maternal asthma and infant’s sex was found, suggesting that a history of maternal asthma was associated with a lower tPTEF:tE% in male infants only. Furthermore, age at test, weight gain and birth order were associated with tPTEF/tE%.

It was possible that the negative effect of maternal asthma history on tPTEF:tE% diminished in female babies in the first weeks of life, said the investigators, pointing to the concept of sexual dimorphism which suggests that lung development in male foetuses may lag behind that of female foetuses in the late stages of gestation.

“Better lung function in male babies is clinically relevant as it is associated with less wheezing in infancy and asthma in childhood, and less severe viral lower respiratory tract infections. Furthermore, lung function trajectories may be established in early life and persist throughout childhood and beyond,” they wrote.

Ongoing follow-up studies of the cohorts will be able to test the hypothesis, they added.