Drastic increase in twins being born in recent years

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  • A new study shows that the number of twins born in recent years has increased significantly
  • The number of twins globally has increased by a third compared to three decades ago
  • Researchers says that medically assisted reproduction is a major contributor to this increase

The number of twins being born is now higher than ever before, according to a recent global overview published in the journal Human Reproduction

In the 1980s, the natural twinning rate was high in African countries, but fairly low in regions like East Asia and South America, and at an intermediate level in Europe and North America.

Researchers of the present study collected information on national twinning rates for two periods:  1980–1985 and 2010–2015. Information for the period 2010–2015 was collected from 165 countries (which make up 99% of the world’s population) and from 112 countries for the period 1980–1985.

Higher death rates

They found that since the 1980s, the twinning rate has increased by a third – going from 9.1 per 1 000 deliveries to 12 per 1 000 deliveries, which equates to approximately 1.6 million twins born every year.

This increase is quite drastic considering that it occurred over a period of just three decades.

“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 Professor Christiaan Monden, first author of the study.

“This is important as twin deliveries are associated with higher death rates among babies and children and more complications for mothers and children during pregnancy, and during and after delivery.”

What caused this increase? 

Professor Monden and colleagues found that the main reason for this increase in twinning – occurring especially in high-income countries – was due to medically assisted reproduction such as IVF (in vitro fertilisation). Rates of twinning were especially high in European, Asian (32%) and North American countries (71%). 

Professor Monden explained: “In both periods, Africa had the highest twinning rates and there was no significant increase over time. However, Europe, North America and the Oceanic countries are catching up rapidly. About 80% of all twin deliveries in the world now take place in Asia and Africa.

“The twinning rate in Africa is so high because of the high number of dizygotic twins born there – twins born from two separate eggs. This is most likely to be due to genetic differences between the African population and other populations.”

According to Professor Jeroen Smits, co-author of the paper, the study highlights important issues relating to levels of twinning in low- and middle-income countries: “Because infant mortality rates among twins have been going down, many more of the twins born in the second period of our study will grow up as twins compared to those born in the early 80s.”

“However, more attention needs to be paid to the fate of twins in low- and middle-income countries. In sub-Saharan Africa in particular, many twins will lose their co-twin in their first year of life, some two to three hundred thousand each year according to our earlier research. 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.”

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