There is a twin birth boom in the world: there are more than 1.6 million a year, and practically one in every 42 twin babies. This is the highest peak in the past forty years, and possibly the entire history of humanity, that has been reached for greater use of medically assisted reproductive technologies as mothers are increasingly aging. This is supported by figures collected in more than a hundred countries by experts working at the University of Oxford, the French Institute for Demographic Studies (INED) and the Dutch University of Radboud. The results are published in the journal Human Reproduction.
The researchers examined the births registered in the period 2010-2015 in 165 countries (covering 99% of the world’s population) and then compared them with those registered in 112 countries in the period 1980-1985. Thus it appeared that the twin birth rate increased by a third from 9 to 12 per thousand. The main driver of this growth is the spread of medically assisted reproductive technologies: not only in vitro fertilization, but also ovarian stimulation and IVF. It was developed in the most advanced countries in the 1970s, then expanded into Asia and Latin America between the 1980s and 1990s, reaching the richest regions of Africa and South Asia after 2000.
Sociologist Christian Monden of the University of Oxford commented: “The relative and absolute numbers of twins in the world are the highest since the mid-twentieth century and are likely to represent a peak at all times.” “Most of the data indicates that we have reached the peak in the richest countries, especially in Europe and North America, while Africa will be one of the main drivers in the coming decades,” explains Jill Besson, a demographic expert at the National Institute for Demographic Studies (INED).
Munden notes that “the overwhelming number of births of twins has increased everywhere except in South America.” “In North America and Africa, the numbers grew by more than 80%, and in Africa this increase was caused by population growth.” Currently, 80% of twin births occur on a global scale between Africa and Asia. “The rate is very high in Africa because many dizygotic twins are born there, or twins that come from two different cells of the eggs,” Munden notes. “This is likely due to the genetic differences that distinguish the African population from others.” Around the world, it is “different twins” that fuel the growth of multiple births, while monozygotic twins remain stable at four births per thousand.
Better knowledge of these numbers, especially in poorer and developing countries, is very important, because “twin births – Mundin adds – is associated with higher newborn and infant mortality and with greater complications for mothers and children. In the later period.” “We need to pay more attention to what will be the fate of the twins in low- and middle-income countries,” concludes Jeron Smits of Radboud University. “In sub-Saharan Africa in particular, many twins lose their siblings in the first year of life, between 200,000 and 300,000 every year.”