What percentage of births are twins?

About 12 in every 1,000 deliveries worldwide are twin births, roughly 1.2%, or about 1.6 million twin pairs a year. That is up by a third since the 1980s, mainly from fertility treatment and older mothers in richer countries. Identical twinning has stayed steady at about 4 per 1,000 deliveries.

Source: Monden, Pison & Smits (2021), Human Reproduction 36(6)