Low Birth Weight and Impaired Later Lung Function: Results from a Monochorionic Twin Study

Area of Science:

• Pulmonology and Respiratory Medicine
• Fetal Medicine and Neonatology
• Pediatric Cardiology

Background:

• Fetal growth restriction (FGR) and low birth weight are known risk factors for impaired lung development.
• Distinguishing the independent effects of gestational age versus fetal growth on lung function is challenging due to their frequent correlation.
• Monochorionic twins with selective FGR offer a unique model to isolate the impact of birth weight on lung development.

Observation:

• A study involving 20 monochorionic twin pairs with selective FGR and discordant birth weights (minimum age 6 years) was conducted.
• The smaller twin (case) and the larger cotwin (control) underwent comprehensive lung function tests (spirometry, plethysmography, multiple-breath washout) and MRI.
• Mean age was 18.4 years, with an average birth weight difference of 575g between twins.

Findings:

• Lower birth weight in the smaller twins was significantly associated with reduced forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) z-scores.
• For every 500g decrease in birth weight, FEV1 z-score increased by 0.50 and FVC z-score by 0.44, indicating a direct relationship between birth weight and lung function.
• Elevated ventilation inhomogeneity in acinar airways (S_acin) was observed in smaller twins and correlated with low birth weight, suggesting impaired small airway function.

Implications:

• Low birth weight, irrespective of gestational age, has lasting detrimental effects on both large and small airway function into early adulthood.
• Intrauterine growth restriction directly impairs lung development, leading to persistent respiratory deficits.
• These findings underscore the importance of monitoring and potential interventions for individuals born with low birth weight due to FGR to address long-term respiratory health.