Gestational age and body size from infancy to adolescence in 16 cohort studies

What is already known about this subject:

• Today, one in ten infants are born preterm (<37 completed weeks’ gestation) with an increased risk of perinatal mortality, and morbidity that may persist and develop over the life-course. Global estimates suggest an increase in preterm birth between 2000 and 2014, but the proportions vary between countries.
• Previous systematic reviews and meta-analyses have reported an association of gestational age at birth (GA) with conventional cardio-metabolic risk factors, including increased blood pressure, impaired glucose regulation, and insulin resistance in those born preterm. An infant born preterm adapts to extrauterine conditions entering a phase of growth that possibly expresses a mismatch with the environment outside utero leading to alterations in body composition. It has been hypothesized that these changes increase susceptibility to being overweight through various pathways and mechanisms, including catch-up weight (16, 18-21). However, later body size in preterm cohorts is not well characterized and the majority of studies defining populations by birth weight rather than actual length of gestation. It is recognized that determinants and consequences of gestational duration are quite different from those of foetal growth (22), and that birth weight reflects both gestational duration and foetal growth (23), hence being at potential intermediate variable on the causal pathway.
• Studies have shown that extremely and very preterm infants typically experience postnatal growth failure followed by catch-up weight and length gain within the first two years of life. Growth in preterm children remains different from that of full term peers through childhood and into school age. However, studies on growth in preterm cohorts across key stages of growth development and at more advanced gestational age are scarce. Several methodological considerations and sample characteristics complicate the interpretation and comparability of findings on the relationship between GA with later body size. This includes differences in study design; using birth weight as a proxy for GA; sample size; age at outcome; conditions under which variables are examined; type of statistical analysis; and availability of confounders.
• In this study, we use the novel approach and unique opportunity of federated analysis of individual participant data in a secure manner provided by the EU Child Cohort Network, an international network of European and from Australia the Raine Study Gen 1 and Gen2 birth cohort data. We base our study on 16 cohorts and 253,810 mother-child dyads, which enables us to extend previous research by including information on repeated body size measures during a long follow-up across a wide range of GA, and take into account the methodological limitations identified above.
• The overall aim of this study was to determine the association between GA (completed weeks and clinical categories) and, respectively, body mass index (BMI) and overweight (including obesity) from infancy through adolescence in birth cohort studies representing diverse contexts.