In 1993, the WHO undertook a comprehensive review of the references, charts and tools used to monitor and evaluate human growth across the world. The conclusion of that review was that the biological and technical drawbacks of the growth resources available at that time were significant, and posed a huge constraint to clinical practice and research. This led to a new and innovative approach to studying large cohorts of multiethnic populations – the Multicentre Growth Reference Study – to inform the world’s first internationally-applicable growth standards: the WHO Child Growth Standards. These standards represent the first evidence-based definition of what normal growth and development for children is, without ethnic or sample size bias. Unlike references of the past, these standards are as applicable in high-income countries as they are in low-income countries. Their use in practice has provided clinicians with a methodologically-sound definition of what a child’s growth should be in order to achieve optimal health outcomes, and for researchers, has provided a common definition of child growth that has standardized investigation in this important area of health.
The impact of the WHO Child Growth Standards on child health and nutrition has been substantial, leading to demands for growth standards throughout the lifecycle. Given the small but growing body of evidence connecting fetal health to newborn, child and adult health outcomes, an international group of researchers have extended the logic of standardization into the perinatal period. The International Fetal and Newborn Growth Consortium for the 21st Century (INTERGROWTH-21st) formed to study healthy pregnancies in multiple geographic locations in order to create evidence-based fetal growth, newborn size, and preterm growth standards for international use.
The current lack of evidence-based growth standards for use during pregnancy and early infancy poses a constraint to practitioners and researchers alike. A 2012 systematic review of methodologies that have been used to create fetal growth charts shows that while the quality of evidence on this topic has improved over time, there remains extreme heterogeneity in study methodology. This diversity in research methods and findings has been subsequently used to inform diverse practical recommendations for fetal growth. All the studies included in this analysis were at high risk for bias due to the lack of rigorous participant inclusion/exclusion criteria, an absence of quality control measures, and the limited evidence of adequate sample size calculations. The authors concluded that international and evidence-based standards for fetal growth, accompanied by the right training and quality control resources, are needed to improve the current state of research and practice.
The INTERGROWTH-21st studies were implemented in eight study sites to create a population-based, multiethnic cohort of 60,000+ pregnancies, with uniform entry criteria, clinical care, equipment, quality control measures, data collection, and methods for collecting anthropometric and ultrasound measurements in each site.