Phenomenon: why is there an unprecedented double boom in the world?

PARIS.- Never before have so many twins been born in the world, a phenomenon due to the spread of assisted reproduction and the advanced age of pregnancies., affirms this Friday a group of researchers.

More than 1.6 million sets of twins are born each year in the world, it is “Almost one in 40 babiesAccording to the study published in the specialized journal Human Reproduction.

Since the 1980s, the global rate of twin births has increased by a third, from 9.1 to 12 per 1,000 deliveries, in just three decades, explains Gilles Pison, professor at the National Museum of Natural History and associate researcher at the National Institute of Demographic Studies (INED), based in France.

This double boom is worrying because they are often born under the correct weight, are premature, have more complications during childbirth and suffer more mortality than others. And that’s beyond the difficulties for parents to take care of two babies at the same time.

The increase in the worldwide frequency of twins is due solely to the unprecedented increase in pregnancies of so-called “fraternal twins” (of two different eggs), which vary from continent to continent and from period to period.

Constant rate

Authentic (monozygotic) twins are born everywhere in the same proportions, with “a constant rate – of four deliveries of genuine twins per 1,000 deliveries – which does not vary with the woman’s age, nor between regions,” Pison explains. .

The Medically assisted reproduction, which began in wealthy countries in the 1970s, has contributed to this increase in multiple births, such as late pregnancies.

The blood level of a hormone involved in egg maturation and ovulation, FSH, increases with age and increases the likelihood of a twin pregnancy, peaking at age 37. From this age (if assisted reproduction is not used), the rate of fraternal twins drops rapidly due to failures in ovarian function and increased embryonic mortality, the researcher explains.

By continents

Technical advances in assisted reproduction have made it possible for years to have a successful pregnancy by implanting a single embryo and freezing the others. This means that “we may have peaked in terms of twinning rates, especially in rich countries,” say the authors.

Study authors Gilles Pison, Christiaan Monden from the University of Oxford and Jeroen Smits from the University of Radboud in the Netherlands used all available data to estimate the rate of twins in different countries and describe changes over three decades., Comparing the periods 1980-1985. and 2010-2015.

Of the 3.2 million twins born each year, 1.3 million are born in Africa (650,000 couples) and as many in Asia. The rest, about 600,000 children, on other continents.

If Asia has so many twin births, it is mainly because it is home to 60% of humanity.

The large number of twins in Africa (17%) is due to a much higher birth rate than elsewhere and because beyond that, he already has the highest rate of twins in the world.

So in Africa, the rate is 17.1 double deliveries per 1000, while in South America it is 9.3 for the period 2010-2015 and in Asia 9.2.

The twin birth rate in Europe and North America 30 years ago was almost half that of Africa, but it has risen sharply (reaching 14.4 and 16.9 twin deliveries per 1

000, respectively).

Agencia AFP

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