Abstract 35: In Singletons Born at Term, Lower Gestational Age is Associated with Lower Cardiorespiratory Fitness Levels Through Adolescence to Young Adulthood: The Northern Ireland Young Hearts Project (NIYHP)

Abstract

Decreases in the mean gestational age of term deliveries have been reported over the past decade in several developed countries, linked to increases in the rates of planned births by labour induction and/or pre-labour caesarean sections. In contrast to the effects of pre-term birth, the extent to which lower gestation age within the at-term range (i.e. 37 to 42 weeks) affects individuals’ cardiorespiratory fitness (CRF) health is largely unknown, however. We therefore examined the association between gestational age, accounting for other important perinatal covariates (obtained from the NI Child Health Services’ records), and CRF (VO 2 max) as measured through adolescence to young adulthood in 842 (51.5% female) participants in the NIYHP (all singletons born at term, 98% of whom with birth weight greater than 2.5 kg). Participants’ mean levels of CRF were 45.6 ± 4.8, 43.7 ± 6.8 and 32.9 ± 9.8 ml/kg/min at the ages of 12, 15 and 22 years, respectively. With the use of GEE analyses adjusted for age, sex, socio economic status, birth weight z-scores (relative to UK’s 1990 reference), breast-feeding practices and duration, maternal age at child’s birth and delivery mode, we found that each week increase in gestational age was associated with 0.44 ml/kg/min (95% CI 0.13 to 0.75) higher levels of CRF throughout the whole longitudinal period (p=0.005). Further adjustments for participants’ height, body fatness and maturational level throughout the longitudinal period only attenuated this association slightly [to 0.38 ml/kg/min (95% CI 0.12 to 0.65), p=0.005]. There were no significant interactions between gestational age and sex or participants’ age at the time of CRF assessment, indicating that the decreases in CRF over time were similar across the different gestational ages, with those born early term displaying consistently lower levels throughout the longitudinal period. Finally, each week increase in gestation age was associated with lower risk of poor CRF through adolescence to young adulthood as defined according to current age and sex-specific health-reference values of VO 2 max: RR=0.89 (95% 0.81 to 0.97), p=0.008. These findings suggest that lower gestational age, even within the at-term range , may be a key determinant of poorer CRF as each additional week conferred benefits. This aspect may have been neglected by the over-simplistic characterisation of individuals born at-term as a homogeneous group and may have public health and clinical implications for policies around planned deliveries, given the current trends.