Study: Early-term births linked to poorer CRF through young adulthood

Longitudinal data from a prospective cohort study indicate that being born early term may negatively affect a child’s cardiorespiratory fitness (CRF). The trend, the authors say, continues into young adulthood and provides another rationale for deterring avoidable deliveries at lower gestational ages.

Published in The Journal of the American Heart Association, the findings are based on analysis of data from participants in the Northern Ireland Young Hearts Study, all of whom were singletons born at term. The prospective cohort study was designed to investigate development of lifestyle and biological cardiovascular risk factors through adolescence to young adulthood. A total of 791 boys and girls aged 12 to 15 were enrolled in 1989 and examined repeatedly until 1999.

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When the participants were aged 12, 15 and 22, their mean levels of CRF were 45.6, 43.7 and 33.0 mL/kg per minute, respectively. After adjustment, each week increase in gestational age was associated with a 0.46 mL/kg per minute increase in CRF (95% confidence interval [CI], 0.14-0.79), or a 14% risk reduction. Those born at 37 to 38 weeks (considered early term by the authors) had a 57% higher incidence of poor CRF (risk ratio, 1.57; 95% CI, 1.14-2.16) than did the participants born at 39 to 40 weeks (full term) or 41 to 42 weeks (late term). Changes in CRF through adolescence to young adulthood were similar across groups, with those born early term consistently displaying lowest CRF.

Confounders considered by the researchers included maternal age, mode of delivery, occupation of the main breadwinner in a child’s family, and birthweight. A parental questionnaire at the study start was used to gather information on breastfeeding duration and maternal height, weight, and smoking history. The authors said adjustments for growth, maturation, and adiposity did not appreciably change their findings.

In commenting on the reasons for the connection between early-term birth and CRF, the authors said that “earlier births may interrupt normal development and lead to permanent changes of tissues and organs, such as fewer alveoli, lower capillary density, and a smaller vascular tree, which, in turn, may lead to long-lasting impairments in maximal oxygen uptake and transport, muscular power, and motor coordination.” They suggested a future research focus on “how current rates of [early term] affect offspring’s CRF in younger cohorts and how these associations may be modified by recent improvement in breastfeeding rates (or deterioration in other postnatal feeding practices).”     

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