Small for gestational age tied to reduced lung function in middle age

Being born small for gestational age (SGA) appears to contribute to a reduced lung function during middle age, reveals a study.

“This suggests that the long-term detrimental effect of reduced foetal lung growth is associated with lower adult lung function which is most likely due to smaller lungs with little evidence of any specific parenchymal impairment,” the researchers said.

A total of 849 participants in the Tasmanian Longitudinal Health Study who had both known birth weight and lung function assessment at 45 years of age were included in this analysis.

The researchers fitted linear regression models to explore the association of SGA and birth weight with postbronchodilator lung function measures (ie, forced expiratory volume in 1 second [FEV₁], forced vital capacity [FVC], FEV₁/FVC, diffusing capacity for carbon monoxide [D_Lco], residual volume [RV], and total lung capacity [TLC]), with adjustments for potential confounders. They also examined the contribution of adult height as a mediator of the above associations.

Participants who were born SGA as infants, compared with those born with normal weight for gestational age, showed reduced FEV₁ (coefficient, −191 ml, 95 percent confidence interval [CI], −296 to −87), FVC (coefficient, −205 ml, 95 percent CI, −330 to −81), TLC (coefficient, −292 ml, 95 percent CI, −492 to −92), RV (coefficient, −126 ml, 95 percent CI, −253 to 0), and D_Lco (coefficient, −0.42 mmol/min/kPa, 95 percent CI, −0.79 to  −0.041]) at age 45 years. [Respirology 2023;28:159-165]

The two cohorts, however, had similar FEV₁/FVC.

Each 1-kg increase in birth weight resulted in an increase in lung function indices by an average of 117 ml (95 percent CI, 40‒196) for FEV₁, 124 ml (95 percent CI, 30‒218) for FVC, 215 ml (95 percent CI, 66‒365) for TLC, and 0.36 mmol/min/kPa (95 percent CI, 0.11‒0.62) for D_Lco, independent of gestational age, but not for FEV₁/FVC. Notably, adult height mediated these associations (56 percent to 90 percent).

“These findings highlight the importance of preventive strategies that aim to reduce factors that predispose to SGA,” the researchers said.

Foetal growth

SGA has been used as a substitute of reduced foetal growth, which may be related to genetic factors or adverse intrauterine exposures, the researchers noted. Reduced foetal growth and low birth weight are associated with maternal smoking, low socioeconomic status, and poor maternal diet during pregnancy, but other factors remain unknown. [J Pregnancy 2013;2013:172395; Lancet 2005;365:891-900]

The current study adjusted for potential confounding by socioeconomic status and parental smoking during pregnancy and gestational age.

“Our findings are consistent with the ‘foetal origins’ hypothesis also known as the ‘Barker hypothesis’, which proposed that impaired intrauterine growth may lead to long-term consequences for many aspects of adult life, including poor physiological function and disease risk,” the researchers said. [BMJ 1991;303:671-675]

“While reduced foetal growth is associated with restrictive lung deficits, prematurity is associated with more obstruction,” they added. [Lancet Respir Med 2022;10:478-484]

Such findings back public health interventions that can improve the average birth weight to boost lung function at a population level. Proposed interventions and preventive measures included improvement of women’s nutritional status and smoking cessation during pregnancy. [BMJ Glob Health 2017;2:e000389; Cochrane Database Syst Rev 2009;Cd001055]

“However, studies evaluating whether attempts to enhance intra-uterine growth have a long-lasting influence on lung health are needed,” the researchers said.