Looking at trends in Brazil and China where there is high use of C-section, the researchers found that many were in low-risk pregnancies, in women who were well-educated, and in women who had previously had a C-section.
Emeritus Professor Gerard Visser, of University Medical Centre Utrecht in the Netherlands, and chairman of FIGO's Committee for Safe Motherhood and Newborn Health, said: "Worldwide there is an alarming increase in caesarean section rates".
"Pregnancy and labour are normal processes, which occur safely in most cases", series lead Dr Marleen Temmerman said in a press release.
The global study, which involved several United Kingdom universities, is being presented at the worldwide Federation of Gynaecology and Obstetrics (FIGO) World Congress in Brazil, where the authors are calling on healthcare professionals, hospitals, women and their families to only intervene with a C-section when it is medically required.
C-sections are considered medically necessary when the duration or logistics of vaginal delivery would put the birth parent or baby in danger - say, in the event of fetal infection - according to the Mayo Clinic.
The information was published by the Lancet in a series of three papers, covering the reasons for the rising use of caesareans around the world, the long-term health risks associated with C-sections, and possible interventions to lower procedure rates. The South Asia region has seen the most rapid increase in use (6.1 per cent per year), with C-section being underused in 2000 but overused by 2015 (increasing from 7.2 per cent of births to 18.1 per cent).
"More research is needed to understand the high frequency of C-section use and its determinants in some countries, and the very low use of C-section in other countries, to provide a more solid basis for interventions towards an optimal frequency of C-section use for mothers and children", the authors write.
Researchers suggest that these disparities may be explained by persistent issues with shortages in healthcare facilities and staff in vulnerable and rural areas - a weakness they say needs to be addressed.
"In cases where complications do occur, C-sections save lives, and we must increase accessibility in poorer regions, making C-sections universally available, but we should not overuse them", she said. There is emerging evidence that babies born via C-section have different hormonal, physical, bacterial and medical exposures during birth, which can subtly alter their health.
While often lifesaving, C-sections aren't without risks, cautions the Lancet report.
However, the surgery is not without risk for mother and child, and is associated with complications in future births, researchers said. That translates to 16 million of the 132 million live births in 2000 and 30 million of the 141 million live births in 2015. In Brazil, for example, 54.4% of women who have completed high-level studies deliver by caesarean section versus 19.4% of women with less education.
"C-section is a type of major surgery, which carries risks that require careful consideration".
The study warned that in many settings young doctors were becoming "experts" in C-section while losing confidence in their abilities when it comes to natural birth.
'The medical profession on its own can not reverse this trend, ' he said.
They also target healthcare professionals, calling for mandatory second opinions and the introduction of clinical practice-based guidelines for when caesarean births are recommended.
Until recently, the World Health Organization (WHO) suggested that Caesarean section - or C-section - rates of more than 15% were excessive.