A landmark international study tracked almost 60,000 pregnancies from a diverse selection of countries that included Brazil, China, India, Italy, Kenya, Oman, the UK and the USA. They found that the babies were overwhelmingly similar in size under the condition that they were born to well-educated mothers in good health who ate well during pregnancy.
This means the global disparity in baby size reflects the health and wealth gaps, rather than race and ethnicity as previously thought.
"Currently we are not all equal at birth. But we can be," says lead author Professor Jose Villar of the Nuffield Department of Obstetrics & Gynaecology, University of Oxford. "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."
The unprecedented scale of the project, which involved the recruitment of almost 60,000 women, standardizing clinical practices and equipment of 300 health professionals across eight study sites and a team of over 200 researchers and clinicians, brought passionate reactions from those involved.
"Don't tell us nothing can be done," says Villar. "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."
Using exactly the same technology in all countries, researchers measured babies' bone growth in the womb by means of ultrasound and found striking similarities across racial and ethnic groups, but within the well-educated, healthy circles.
The mean length at birth of the newborns was 49.4 ± 1.9 cm.
Researchers concluded that only four percent of size disparities could be accounted for due to race and ethnicity.
According to the study the diversity of the many growth charts -- over 100 of them -- used to track newborns the world over is a problem, and needs to be standardized like the one for children.
"This is very confusing for doctors and mothers and makes no biological sense," says Professor Stephen Kennedy, University of Oxford, one of the senior authors of the paper. "How can a fetus or a newborn be judged small in one clinic or hospital and treated accordingly, only for the mother to go to another city or country, and be told that her baby is growing normally?"
This study, called the INTERGROWTH-21st, was inspired by a similar study by the World Health Organization, called the Multicentre Growth Reference Study, which standardized the growth charts for children now used in 140 countries.
The INTERGROWTH-21st study, led by a team of researchers from Oxford University, now aims to set the standard for fetal growth and newborn size according to proper health and nutrition on the part of the mother.
"Just think, if your cholesterol or your blood pressure are high, they are high regardless of where you live. Why should the same not apply to growth?" says Professor Villar.
Researchers have high hopes that the surprising results of their study will encourage better maternal health on a global level.
"The fact that when mothers are in good health, babies grow in the womb in very similar ways the world over is a tremendously positive message of hope for all women and their families," says Professor Zulfiqar Bhutta, from The Aga Khan University, Karachi, Pakistan and the Hospital for Sick Children, Toronto, Canada, who is the Chair of the Steering Committee of this global research team.
With projects already underway such as Maternal Alliance for Mobile Action (MAMA), which telecommunicates healthcare advice to moms and moms to be in countries such as Bangladesh with reduced access but high mobile phone consumption, it's possible that change could come about quickly in some places.
According to Bhutta, communication is only half the battle, and the real challenge lies in changing the beliefs and habits among health professionals.
"There are implications in terms of the way we think about public health: This is about the health and life chances of future citizens everywhere on the planet," says Bhutta. "All those who are responsible for health care will have to think about providing the best possible maternal and child health."
The study was published in the journal The Lancet.