Frequently Asked Questions

Frequently Asked Questions about the INTERGROWTH-21^st Project

What is the INTERGROWTH-21^st Project?

The International Fetal and Newborn Growth Consortium for the 21^st Century, or INTERGROWTH-21^st, is a global, multidisciplinary network dedicated to improving perinatal health.  Established in 2009 at the Oxford Maternal and Perinatal Health Institute, Green Templeton College, University of Oxford, the network has since grown to more than 300 researchers and clinicians from 27 institutions in 18 countries worldwide, constituting the largest collaborative venture in perinatal health research.  With the generous support from the Bill & Melinda Gates Foundation, the INTERGROWTH-21^st network conducted an extremely rigorous prospective, population-based study of fetal and newborn growth involving 60,000 women and newborns across eight study sites in five continents over five years, with two-year follow-up of babies still ongoing.

Why is fetal and newborn growth important?

Fetal and newborn growth is an important indicator of an individual’s health and well-being across the life course. An adverse intrauterine environment, i.e., poor nutrition and infection, may impair growth of the fetus. Intrauterine growth restriction (IUGR) is the leading cause of stillbirth and in those that survive pregnancy, it has a profound effect on an individual’s health and well-being in the short and long-term. Studies have shown that growth restricted babies are more susceptible to infection in the first weeks of life, and are more likely to develop diabetes, hypertension and cardiovascular disease later in life.  

What tools are currently available to measure fetal and newborn growth?

Fetal and newborn growth is currently measured using cross-sectional, population-based references that vary by setting and country. A systematic review conducted by INTERGROWTH-21^st researchers identified major discrepancies in median values and percentile curves of key anthropometric variables due to: biological and social determinants of the study populations, diversity of study design, methodologies and data presentation in current growth charts.

Why are current methods of measuring fetal and newborn growth problematic?

Current measures of fetal and newborn growth are problematic because they lack:

• Rigorous participant inclusion/exclusion criteria;
• Quality control measures to avoid observer error;
• Evidence of adequate sample size calculations.

What are prescriptive growth standards?

A prescriptive approach describes how growth should occur when conditions for growth are optimal rather than how growth has occurred in a particular time or place. For the INTERGROWTH-21^st growth standards data were collected longitudinally using a carefully selected multiethnic, population-based sample. The participants were healthy, well-nourished mothers who experienced minimal environmental constraints on growth. There was early evaluation of gestational age confirmed by ultrasound examination before 14 weeks. Measurements throughout pregnancy and feeding practices and newborn care after birth were uniform across the study centers. INTERGROWTH-21^st also applied a strong scientific foundation via rigorous inclusion/exclusion criteria.

What is different about the way the INTERGROWTH-21^st Project approaches the measurement of fetal and newborn growth?

The care and measurements performed at all eight study sites were standardized to ensure homogeneity of clinical practices among the sample of nearly 60,000 mothers and babies. All study sites followed the same anthropometry and ultrasound procedures to measure newborns. This resulted on more consistent fetal and newborn measurements between study sites than those shown on previous research..

How does the INTERGROWTH-21^st Project define normal, healthy growth?

From the INTERGROWTH-21^st Project, the distributions for optimal fetal and newborn measurements for each week of gestation have been established with percentile values and z-scores defined. Babies born to mothers that developed severe pregnancy complications (e.g eclampsia, malignancy) or babies with severe adverse outcomes (death or congenital malformation) were excluded from this group.

What are the main findings of the INTERGROWTH-21^st Project?

If mothers are healthy at the start of pregnancy, live in environments free from external constraints on growth, have access to regular evidence-based healthcare and breast feed, their children have similar linear growth patterns from 9 weeks post-conception until birth irrespective of nationality and ethnicity. Optimized conditions for fetal, infant and child development can change height, weight, growth and cognitive potential within a generation.

Are the INTERGROWTH-21^st growth standards applicable to all women and babies?

Yes. A prescriptive standard provides a benchmark against which the growth of all babies in the world can be compared. Whilst obviously most babies will not fall on the 50^th centile or have a z-score of 0 for gestational age, the further away from the optimal size that they are, the higher the likelihood that there has been some degree of intrauterine growth problem. This should prompt health care providers to look carefully at the mother’s health and nutrition and alert them to the increased risk faced by the baby. The new fetal and newborn growth standards will be as applicable in settings where women are under-nourished and children are wasted and stunted as they are in settings where women and children are over-nourished. This is of particular importance in settings where low-nutrient and high-calorie foods are becoming more and more accessible. Introduction of these foods greatly increases the number of women who are overweight and obese entering pregnancy and at higher risk of pregnancy complications, such as preeclampsia and gestational diabetes.

In addition to the new global growth standards, what other clinical tools is the INTERGROWTH-21st Project producing?

The INTERGROWTH-21^st Project is producing a range of tools to improve the monitoring and recognition of poor fetal growth and development. These include phenotypic classifications for babies born small or preterm, weight gain and symphysio-fundal height standards for pregnant women as well as standards for preterm growth, feeding patterns and neurodevelopment.

Are the INTERGROWTH-21^st tools only for doctors to use?

No. The standards will be important for other health care providers caring for pregnant women and newborns as well as the research community and parents concerned about their own child’s development.

Do all of the INTERGROWTH-21^st tools require the use of an ultrasound machine?

No. Standards for measurement of the newborn and weight of the mother during pregnancy do not involve ultrasound. However in order to correctly interpret the standards, accurate knowledge of gestational age is essential therefore if ultrasound is available, use of the INTERGROWTH-21^st standards through ultrasound is strongly recommended.

How can the INTERGROWTH-21^st growth standards improve clinical practice and research, as well as maternal, newborn and child health programs?

The INTERGROWTH-21^st standards will improve the recognition of babies that have failed to reach their growth potential and provide a practical grading of the degree of growth disturbance that is present, compared to an optimal, international standard. This will improve both the counting and recognition of babies with growth problems, enabling a valid comparison of outcomes between and within countries. Clinical research about fetal growth and development to date has been extremely heterogeneous, with no consensus on what constitutes normal and abnormal growth and development. A universally applicable tool can allow for the foundation of consistent and generalizable research findings. In addition, the new growth standards provide a screening tool for communities to monitor growth and development and identify those who are at higher risk to develop stunting and impaired cognitive development. Clinical and public health practitioners must address specific factors that influence abnormal fetal growth within their population at the local-level.