It shows in 2010/11 there were just less than 20 deaths for every 100,000 births, compared with just less than ten deaths six years previous.
The increase is being put down to a shortage of midwives, along with rising birth and obesity rates and women delaying motherhood.
There are no equivalent figures for the rest of the UK, but it is believed that the trend is likely to be replicated across other locations.
Cathy Warwick, RCM chief executive, said: ‘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.’
She added that while the maternal mortality rate was most acute London, it is likely to be replicated in other areas, especially cities.
The Centre for Maternal and Child Enquiries is the national body that would previously have analysed data on maternal deaths.
However, the centre has had its work suspended for just over a year, to save cash amid the reorganisation of NHS services.
Dr Susan Bewley, consultant obstetrician from Guy’s and St Thomas’ hospital in London, said: ‘We do know women are becoming pregnant when they are older and fatter and have more complex health issues.
‘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.’
The RCM’s e-petition
for 5000 more NHS midwives has now almost reached 40,000 signatures.
To force politicians to consider the issue, it must reach 100,000 by 22 August this year (2012).
The study is published in The Lancet