It has previously been suggested that 'race' and 'ethnicity' are largely responsible for differences in the size of babies born in different populations and countries.
But a landmark study led by Oxford University researchers has shown that growth of babies in the womb and their size at birth, especially their length, are strikingly similar the world over - when babies are born to healthy, well-educated and well-nourished mothers.
The study involved almost 60,000 pregnancies in eight defined urban areas in India, China, Brazil, Italy, Kenya, Oman, the United States and Britain.
"Currently we are not all equal at birth. But we can be," said the lead author professor Jose Villar from University of Oxford in Britain.
"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," he added.
"Do not say that women in some parts of the world have small children because they are predestined to do so. It is simply not true," Villar noted.
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The researchers carried out ultrasound scans from early pregnancy to delivery to measure babies' bone growth in the womb, using identical methods in all countries and the same ultrasound machines.
They also measured the length and head circumference of all babies at birth.
If mothers' educational, health and nutritional status and care during pregnancy are equally good, babies will have equal chances of healthy growth in the womb and future good health.
The findings give credence to the chorus calling for international standards to evaluate fetal growth and newborn size.
Foetal growth and newborn size are currently evaluated in clinics around the world using at least 100 different growth charts.
The findings appeared in the journal The Lancet, Diabetes & Endocrinology.