Women should only give birth by Caesarean section if it is medically necessary, the World Health Organisation (WHO) has warned.
The global health body issued guidance suggesting the "ideal rate" of Caesarean births was between 10% and 15%, suggesting unnecessary operations could be "putting women and their babies at risk of short and long-term health problems".
Around one in four babies are born each year by Caesarean section in the UK, according to the latest figures, and current National Institute for Health and Clinical Excellence (Nice) guidelines allow for expectant mothers to choose to have one, irrespective of need.
The WHO cited United Nations-backed studies suggesting there is "no evidence" the death rate decreases when the C-section rate goes beyond 10% of births.
In a statement, it warned "Caesarean sections can cause significant complications, disability or death, particularly in settings that lack the facilities to conduct safe surgeries or treat potential complications.
"Across a population, the effects of Caesarean section rates on maternal and newborn outcomes such as stillbirths or morbidities like birth asphyxia are still unknown. More research on the impact of Caesarean section on women's psychological and social well-being is still needed.
"Due to their increased cost, high rates of unnecessary Caesarean sections can pull resources away from other services in overloaded and weak health systems."
Dr Marleen Temmerman, director of WHO's Department of Reproductive Health and Research, said: "These conclusions highlight the value of Caesarean section in saving the lives of mothers and newborns.
"They also illustrate how important it is to ensure a Caesarean section is provided to the women in need - and to not just focus on achieving any specific rate.
"We urge the healthcare community and decision-makers to reflect on these conclusions and put them into practice at the earliest opportunity."
Figures released by the Health and Social Care Information Centre (HSCIC) in January showed 26.2% of UK births were by C-sections last year.
Overall, the number of women having Caesarean sections has increased over the past two decades, rising from 15% of deliveries in 1993 to 1994.
The operations are often carried out when there are complications with a natural delivery, such as prolonged labour or the baby being in an abnormal position, but some are pre-planned.