The number of twins born since the 1980s has increased 30% to 1.6 million pairs each year. What is driving the increase of twin births at a time when the world is concerned about overpopulation?
More twins than ever before in human history being born
A new study out of Oxford has been published in the journal Human Reproduction, which asked the question, “How many twins are born in human populations and how has this changed over recent decades?”
The answer, it turns out, is: More than ever before in history.
The study found that since the 1980s, the twinning rate around the globe “has increased by a third, from 9.1 to 12.0 twin deliveries per 1000 deliveries, to about 1.6 million twin pairs each year.”
A lot was already known about natural twinning rates around the world. For example, in the 1980s, the rate of twins was low in East Asia and South America. Europe and North America were at an intermediate level at the time. The highest level of natural twinning was occurring in many African countries.
But all that changed in recent decades. Twinning rates have been increasing, particularly in the wealthier parts of the world.
What is causing more twin births?
The study unveiled several factors that have driven the dramatic increase in twinning. Especially in wealthier countries, two factors were most prominent: Medically assisted reproduction (MAR) and delayed childbearing.
Where are the greatest numbers of twins being born?
Currently, 80 percent of all twin deliveries around the globe occur in Asia and Africa. Even before medically assisted delivery became more commonplace and prior to the 1980s, Africa led the world in twin births. Those numbers haven’t changed much over the past thirty years, the BBC reported.
“The twinning rate in Africa is so high because of the high number of dizygotic twins – twins born from two separate eggs – born there,” said Professor Christiaan Monden of the University of Oxford, lead author of the study. “This is most likely to be due to genetic differences between the African population and other populations.”
The study called Nigeria the “twinning champion of the world.”
More twins being born in wealthy countries
In other places around the world, particularly in Europe, North America, and Oceanic countries, the birthrates of twins have been catching up to Africa. This is largely due to the increased use of medically assisted reproduction, which began in the 1970s through IVF, ICSI, artificial insemination, and ovarian stimulation, which have been the driving forces.
According to medical experts, these techniques all increase the likelihood of multiple births occurring.
Another major factor is that women, particularly in wealthier countries, have chosen to start families later in life.
The dangers of multiple births
One thing that concerns medical professionals is that multiple births, such as twins, are “associated with higher infant and child mortality rates and increased complications for mother and child during pregnancy and during and after delivery,” according to the study.
The study authors wrote: “The strong increase in number of twin births due to MAR started to raise concerns in the 1990s among medical authorities and policy makers, because of the public health problems related to twin births. Twins are a high-risk group associated with complications during pregnancy, at birth and thereafter, including preterm deliveries, lower birth weight, increased still births and infant and maternal mortality.”
