MINUTES ON... Twins

When my twin granddaughters were born 14 years ago we were seeing twins in one in 80 births. Now it’s one in 42. What’s going on? A report by Christiaan Monden of Oxford University in the BMJ goes some way to explain.

What’s causing the increase?

One major factor is IVF (medically assisted reproduction) becoming more common. There has also been a considerable effect from women delaying their families because twins are more common when mothers are older.

Is it the same everywhere?

No, there are clear differences. Across 122 countries, the twinning rate has increased 10% in 83 countries, and fallen 10% in seven. The biggest increases were in North America (71%), Europe (58%) and Asia (31%).

What’s happening in Africa?

Twins have always been common there, with little change in 30 years. Monden says the reason is “the high number of dizygotic twins [twins from two eggs] born there — most likely to be due to genetic differences between the African population and other populations.”

Are we peaking out?

We could be, though Africa will be one of the main drivers of twins in the coming decades, says Gilles Pison of the French Museum of Natural History. But he adds: “Advances in IVF make it more likely than not we will see fewer twin births as a result of IVF.”

Are twin births safe?

Here, twin births are safer than ever, but not so in some low and middle-income countries, such as in sub-saharan Africa, where up to 300,000 babies born as a twin are thought to die during the first year of life.