Healthy mothers across the globe give birth to similar sized babies, suggesting nutrition and health, not race and ethnicity affect fetal growth and newborn size.

Previous studies suggest race and ethnicity are two primary factors that can best explain the wide disparities in the average size of babies at birth across the globe. Debunking this hypothesis, researchers of a new study found that nutrition and health have a bigger influence on fetal growth and newborn size.

The research included the analysis of 60,000 pregnancies in eight urban areas in Brazil, China, India, Italy, Kenya, Oman, the UK and USA. For the study, researchers from the University of Oxford performed ultrasound scans on expecting mothers from early pregnancy to delivery. This allowed researchers to record babies' bone growth in the womb. To ensure accurate results, researchers used the same ultrasound machines provided by Philips Healthcare in all countries. They also measured the length and head circumference of all babies at birth.

The researchers found that a mother's educational, health and nutritional status and care during pregnancy were bigger influencing factors than race and ethnicity when it came to newborn size.  If these factors were equally good across the globe, there's a high possibility that babies in different countries will be born in similar sizes.  The researchers also pointed out that less than 4 percent of the total difference in fetal growth and birth size could be attributed to race and ethnicity in the eight studied areas.

"Currently we are not all equal at birth. But we can be," said the lead author Professor Jose Villar of the Nuffield Department of Obstetrics & Gynaecology, University of Oxford, in a press statement. "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 tell us nothing can be done. 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."

In 2010, an estimated 32.4 million babies were born undernourished in low-to-middle-income countries, representing 27 percent of all live births globally. Currently, fetal growth and the size of newborns are evaluated in clinics around the world using at least 100 different growth charts.

"This is very confusing for doctors and mothers and makes no biological sense," said Professor Stephen Kennedy, another member of the Oxford team. "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?"

Small size at birth is associated with infant death and illness, as well as increased risk of diabetes, high blood pressure and heart disease in adult life.

Findings were published online in The Lancet, Diabetes & Endocrinology. The study was funded by the Bill & Melinda Gates Foundation.