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 49.4cm, an international study found.
It was previously 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 4pc 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 measured.
Prof Jose Villar of Oxford University said: "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 women in some parts of the world have small children because they are predestined to do so. It's not true."