Even though they are considered full-term, babies born at 37 to 38 gestational weeks could be more likely to have poor cardiorespiratory fitness (CRF) into young adulthood than those born later.

This finding, published online Sept. 27 in the Journal of the American Heart Association, resulted from an analysis of 791 participants in a Northern Ireland-based study. All participants were born in the full-term range (37-42 weeks) and completed standardized fitness tests at ages 12, 15 and 22 to measure maximal aerobic capacity.

Compared to the other full-term births, those born at 37 to 38 weeks demonstrated a 57 percent higher risk of developing poor CRF. In addition, each week increase in gestational age was associated with a 14 percent risk reduction of poor CRF.

“We believe that earlier births—even within the at-term range—may interrupt normal development and lead to permanent changes of tissues and organs, thereby affecting cardiorespiratory fitness,” Isabel Ferreira, PhD, lead study author and associate professor at The University of Queensland in Australia, said in a press release. “As such, recent trends towards deliveries at shorter gestational lengths within the at-term period are worrisome.”

Ferreira and colleagues pointed out CRF is a major determinant of metabolic and cardiovascular health throughout life. Therefore, enacting policies to eliminate “avoidable deliveries at lower gestational ages”—via caesarean sections or induced labor—could decrease the subsequent burden of cardiovascular disease in future generations, they wrote.

The authors noted their results came from a cohort of white individuals born in the 1970s in a region with a high prevalence of cardiovascular disease.

“Caution may, thus, be warranted when extrapolating our findings to other regions/countries, ethnicities, and/or younger birth cohorts,” Ferreira et al. wrote. “Investigation of how current rates of (early terms) 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) may constitute an important future research agenda.”