The clamour for caesarean sections on demand could lead to more maternal and newborn illness and death, a massive new study suggests.

C-section rates are increasing worldwide, with one in four newborns in Canada now being delivered via an incision in its mother's belly, compared to 17 per cent in the early 1990s.

But a new World Health Organization-led study involving more than 97,000 deliveries in Latin America found that hospitals with the highest rates of caesareans had higher rates of maternal death and severe illness and had higher numbers of babies who died or were admitted to intensive care for seven days or more after birth.

The results, published online by the journal The Lancet, "show how a medical intervention or treatment that is effective when applied to sick individuals in emergency situations can do more harm than good when applied to healthy populations."

While the study involved Latin American hospitals, the researchers believe the findings would hold true "beyond the participating institutions."

Despite years of pressure on doctors to perform fewer, not more, C-sections, the rate is climbing. According to the Lancet article, rates of caesarean deliveries have jumped from about five per cent in developed countries in the early 1970s to more than 50 per cent in some regions of the world.

The World Health Organization says any rate higher than 15 per cent is inappropriate. The rate is nearly double that in Vancouver and some other Canadian cities, according to a report last month by the Canadian Institute for Health Information. In Ontario, the rate is about 24 per cent.

Improved surgical and anesthetic techniques, doctors' fears of lawsuits should a vaginal birth go wrong and patient demand are driving the rise in C-sections. The operation is also thought to reduce the risk of urinary incontinence and "sexual dissatisfaction, (thus) increasing its appeal," write Dr. Jose Villar, member of a WHO and World Bank special program in human reproduction, and his colleagues.

The new study is believed to be the largest of its kind exploring the association between C-sections and bad outcomes for mothers and babies.

Scientists looked at all women admitted for a delivery over three months to 120 private and public hospitals in Argentina, Brazil, Cuba, Ecuador, Mexico, Nicaragua, Paraguay and Peru.

They obtained data for 97,095 deliveries. The median rate of caesarean sections was 33 per cent, with half done for elective, or non-emergency reasons. The rate was even higher (51 per cent) in private hospitals.

The team found that the more elective C-sections a hospital performed, the higher the rates of severe maternal illnesses or death.

Other studies have suggested C-sections are safer for babies. The Lancet study found the opposite to be true. The rates of pre-term delivery and newborn deaths rose with the increasing rates of caesareans.

The researchers are preparing a similar survey for Canada.