Researchers from the National Institute for Demographic Studies (INED) analyzed demographic data across multiple countries to track twin birth trends over the past three decades.
The world is experiencing a remarkable "twin boom," as detailed in a March 12, 2021, study published in Human Reproduction. Approximately 1.6 million pairs of twins are born annually worldwide—about one in every 40 newborns. Lead author Gilles Pison from INED notes that the global twin birth rate has risen by a third since the 1980s, from 9.1 to 12.0 per 1,000 deliveries. This surge raises concerns, as twins are often premature, lower birth weight, and face higher risks of complications and mortality during delivery. Families also face added challenges with the unexpected arrival of two infants.
The rise stems primarily from increased fraternal twin pregnancies (from separate eggs), with variations by continent. Identical twins (monozygotic) remain steady at about four per 1,000 deliveries globally. This trend accelerated in the 1970s with the advent of medically assisted procreation (MAP). Higher follicle-stimulating hormone (FSH) levels, which promote egg maturation and ovulation, boost twin chances up to age 37—levels not previously sustainable due to ovarian decline and higher embryonic loss.
Advances in assisted reproduction, such as single-embryo transfers and freezing surplus embryos, have driven peak twinning rates, particularly in high-income nations.
By comparing 1980-1985 and 2010-2015 data, scientists found that of the 1.6 million annual twin pairs, 1.3 million originate from Africa and Asia (evenly split). The rest are distributed globally. Asia's high numbers reflect its 60% share of the world's population, while Africa's elevated fertility rates contribute significantly. Three decades ago, Europe and North America's twinning rates were nearly half of Africa's. Today, at 14.4 and 16.9 per 1,000 deliveries respectively, they've nearly matched Africa's 17.1.
