In a recent study, researchers gathered demographics from many countries. The goal? Provide an overview of the changes that have taken place over the past three decades in twinning births.
The “twins boom”
Today the world is facing a real “twin boom”. According to a study published in the journal Human reproduction March 12, 2021, approximately 1.6 million pairs of twins come into the world each year, or about one in forty newborns. As explained by Gilles Pison, of the National Institute of Demographic Studies (INED) and one of the lead authors of the study, the global rate of twin births has increased by a third since the 1980sfrom 9.1 to 12.0 per thousand deliveries in just three decades. This boom induces a worrying situation. Indeed, these twins are often premature, lighter and face more complications during childbirth as well as higher mortality. In addition, the arrival of twins is often complicated for families, who expect to welcome only one child.
The increase in the frequency of twins worldwide is due to the rise in fraternal twins (from two different eggs). Moreover, this unprecedented increase varies from one continent to another. As regards identical twins (monozygotes), they are born everywhere in the same proportions, at the rate of four per thousand deliveries. This increase in multiple births and later pregnancies began in the 1970s with the advent of assisted reproduction (ART). However, the blood level of follicle stimulating hormone (FSH) acting on the egg (maturation) and ovulation increases the possibility of having twins. up to the maximum age of 37. Previously, the failure of ovarian function and increased embryonic mortality did not allow this.
Europe is catching up with Africa in terms of twinning
For several years, advances in ART have enabled this success thanks to the implantation of a single embryo. Surplus embryos are frozen. For researchers, this precaution has made it possible to achieve highs in twinning rate, especially in rich countries.
Scientists evaluated the changes in the twinning rate by comparing two periods: 1980-1985 and 2010-2015. Of the 1.6 million pairs of twins coming into the world, 1.3 million pairs are from Africa and Asia (equally). The remaining 300,000 pairs are distributed in other areas of the globe.
Asia has a significant number of twins because this continent is home to 60% of the world’s population. In the case of Africa, the birth rate is much higher than on other continents. Three decades ago in Europe and North America, the twinning rate was almost half that of Africa. With rates of 14.4 and 16.9 per thousand deliveries, these two countries have now practically reached that of Africa (17.1).