Low birthweight and maternal smoking as predictors of infant lung function from a South African birth cohort within low socioeconomic communities

Background. Early assessment of infant lung function (ILF) is necessary to improve our understanding of factors that determine long- term respiratory health. Objective. To identify predictors of lung function among infants aged 6 weeks, 6, 12 and 24 months, from low socioeconomic settings, enrolled within the Mother and Child in the Environment (MACE) study. Methods. ILF tests were performed assessing multiple breath washout and tidal breathing during spontaneous sleep. Several risk factors, relating to infant growth, maternal and environmental exposures, were assessed cross-sectionally against the lung function parameters in multivariable models for each age group. Results. Maternal smoking during pregnancy affected the ratio of time to peak expiratory flow, showing a decline across the age groups, while being statistically significant (β (95% confidence interval (CI)) at 6 weeks (–24.6% (–43.92 - –4.59)) and 12 months (−12.68 (−25.25 - −0.11)). Low birthweight was associated with a lower tidal volume at 6 weeks (−5.99 mL (–9.59 - –2.39)), 6 months (−15.02 mL (−22.48 - −7.57)) and 12 months (−23.7 mL (−35.55 - −11.85)), compared with those with normal birthweight. This was further observed for minute ventilation at 6 weeks (−157.78 mL/min (−338.95 - 23.38)), 6 months (−325.57 mL/min (–619.06 - −32.08)) and 12 months (−527.58 mL/min (−947.85 - −107.32)), though less evident at 24 months. Conclusion. Low birthweight was the main predictor for low tidal volumes and minute ventilation at 6 weeks, with smaller differences observed at 12 and 24 months. Lung function development early in life is primarily driven by infant size and postnatal growth factors, consistent with other studies.