Researchers analysed records from more than 100 countries and found a substantial rise in twin birthrates since the 1980s, with one in 42 people now born a twin, equivalent to 1.6 million children a year. According to the study, the global twin birthrate has risen by one-third, on average, over the past 40 years.
Rather than seeing the trend continue, the world may have reached “peak twin”, the authors say, as the most recent data suggest some countries have begun to see twinning rates plateau or even fall from historic highs.
While the birthrate for identical twins has barely changed over time, [sociologist Christiaan] Monden and his colleagues found that naturally conceived, non-identical twins and twins born as a result of medically assisted reproduction – an umbrella term for a range of fertility treatments – had risen globally.
The main drivers are increased access to hormone treatment, IVF and other fertility services but also the postponement of parenthood – the chances of having natural, non-identical twins increases with age and peaks at 35 to 39 years old.
“It doesn’t surprise us that twinning rates have increased because the availability of assisted reproduction has increased and also because women are slightly older when they have their first children, and both those things will increase the twin rate,” [said gynecologist Raj Mathur.]