A new study published Friday in the University of Oxford science journal Human Reproduction revealed that more twins are being born around the world than ever before. It is the first comprehensive global twinning study ever carried out. 

The research shows that 1.6 million twins are being born every year, which is almost one in 40 children. The record number of births is found in non-identical twins, which come from two separate fertilized eggs. Birth rates of identical twins have remained the same. 

The sample size of the study comprised 165 countries between 2010 and 2015. Researchers also obtained data from 112 countries on twinning rates between 1980 and 1985.

"The relative and absolute numbers of twins in the world are higher than they have ever been since the mid-twentieth century and this is likely to be an all-time high," said Christiaan Monden, the lead author of the study.

The highest number of twin births in both periods was found in Africa. Monden said this is likely to be due to "genetic differences" between the African population and other populations.

Why are more twins being born?

The rise of medically assisted reproductive technologies, such as in-vitro fertilization, is a leading factor for the increase in twin births, according to the research.

The study also said that more mothers are giving birth at an older age, which has been connected with increased twinning rates.

Lower overall fertility rates have also contributed to an increase in twin births. 

"Most data suggest we are at a peak in high-income countries, especially Europe and North America. Africa will be one of the main drivers in the coming decades," said co-author Gilles Pison. 

More twins in poorer countries

Monden said that the increased number of twin births in poorer countries was a matter of concern. 

"Twin deliveries are associated with higher death rates among babies and children and more complications for mothers and children during pregnancy ... during and after delivery," he said.

Jeroen Smits, another co-author, added that in sub-Saharan Africa, many twins lost their co-twin within the first year of birth.

"While twinning rates in many rich Western countries are now getting close to those in sub-Saharan Africa, there is a huge difference in the survival chances," Smits said.