Newborn babies born to healthy, well nourished mothers are strikingly similar in size the world over, scientists have shown.
On average, they have a body length of 49.4 centimetres, an international study found.
Previously it was suggested that ethnicity was largely responsible for the widespread variation seen in the size of babies born around the world.
The new research suggests race and ethnicity contribute little to baby size. What matters more is the education, health and nutrition of mothers, and the care they receive during pregnancy.
Overall no more than 4% of differences in foetal growth and birth size could be attributed to population differences.
Scientists taking part in the Intergrowth-21st study looked at almost 60,000 pregnancies in urban areas of the UK, US, Brazil, China, India, Italy, Kenya and Oman.
Ultrasound scans were carried out to assess babies’ bone growth in the womb, and at birth every infant had its body length and head circumference measured.
Lead researcher Professor Jose Villar, from the Nuffield Department of Obstetrics and Gynaecology at Oxford University, said: “Currently we are not all equal at birth, but we can be. We can create a similar start for all by making sure mothers are well educated and nourished, by treating infection and by providing adequate antenatal care.
“Don’t say that women in some parts of the world have small children because they are predestined to do so. It’s simply not true.”
Findings from the study, funded by the Bill & Melinda Gates Foundation, are reported in the journal The Lancet Diabetes & Endocrinology.
In 2010, an estimated 32.4 million babies were born undernourished in low-to-middle-income countries, representing 27% of all live births globally.
Small size at birth is associated with infant death and illness, as well as increased risks of diabetes, high blood pressure and heart disease in adult life.
Currently foetal growth and the size of newborns are evaluated in clinics around the world using at least 100 different growth charts.
The ultimate aim of Intergrowth-21st is to provide international standards describing the ideal growth of a baby in the womb and from birth to five years of age.