A UK study found that the number of women who have died giving birth in London has doubled in the last five years, twice the maternal death rate of the rest of the country.

Other wealthy countries like Austria, Canada, Denmark, the Netherlands, Norway, and the USA have also seen increases in maternal mortality, according to researchers.

The findings, published in The Lancet, found that between 2005 and 2011, maternal deaths increased from 10 to 20 per every 100,000 women, and in London maternal deaths nearly tripled in the same period of time, from 11 in 2005 to 31 deaths in 2011.

Experts say that the obesity, delayed motherhood, women giving more births to children and use of fertility treatments, which increases the likelihood of giving birth to twins or triplets leading to complex pregnancies, could play a part in the growing number of women dying in labor.

Dr. Susan Bewley, consultant obstetrician from Guy’s and St Thomas’ hospital in London called for “urgent attention,” in light of London’s dramatic rise in maternal deaths, according to The Telegraph.

However she stressed that while the overall numbers on maternal mortality were low in the UK and subject to fluctuations, the rising cases warranted detailed analysis.

"These are bald figures, there is a lot about them that we don't know. We do know that women are becoming pregnant when they are older and fatter, and have more complex health issues,” Bewley said, according to The Telegraph. "It could be that hospitals in London are actually coping surprisingly well against greater odds, or it could mean there are problems with the services," she said.

Bewley said that the country’s maternity services are struggling as birth rates are on the rise.

Researchers noted that while births in London have increased by 27 percent in the last decade from 106,000 in 2001 to 134,000 in 2011, the numbers of midwives and obstetricians have remained the same.

A separate study found that many of the maternal death cases in London happened because the junior doctors were not correctly supervised or overestimated their abilities.

"Across the country, two factors are combining: maternity services are under pressure from a steadily rising birth rate while dealing with far more women with complex pregnancies," said Professor Cathy Warwick, general secretary of the Royal College of Midwives, according to The Telegraph.

Researchers recommend that the UK maternity service be “closely monitored and aligned to need and evidence,” they wrote. “New thinking and more innovative public health measures, supported by government policy, might be required to address maternal risk,” the authors concluded.