Rates of caesarean section births almost doubled between 2000 and 2015 — from 12 to 21 percent worldwide — new research has found, with the life-saving surgery unavailable to many women in poor countries while often over-used in richer ones.

The research, published in The Lancet medical journal on Thursday, found that 60 percent of countries overuse C-sections and 25 percent under-use them, suggesting that recommendations for their use in cases of medical need are widely ignored.

In at least 15 countries, more than 40 percent of all babies born are delivered by C-section. The highest rate, of 58.1 percent, was in the Dominican Republic.