According to Confidential Enquiry into Maternal and Child Health, more mothers died from pregnancy and childbirth in 2003-05 than in 2000-02, when the figure was 261. The death rate is also believed to have increased slightly.
Doctors blame the factors, which include increased rates of obesity among pregnant women and higher numbers of immigrant women who fail to attend antenatal appointments.
Immigrants are more likely to have health problems that result in childbirth complications.
According to doctors, the trend for women to have babies later in life could have contributed to the increase.
However, some medical staff and patient groups are also afraid that the NHS's policy to encourage 'natural' birth without medical assistance is putting women at risk by refusing them medical care in pregnancy and labour.
"Nature dictates that one in every 100 women will die while having a baby. The mortality rate in parts of Africa is now about 850 to 1,000 per 100,000. Left to nature that is what nature will do. I believe in women having choice but it has got to be informed choice," Times Online quoted Professor James Dornan, director of foetal medicine at the Royal Maternity hospital in Belfast, as saying.
The findings follow studies that reveal the UK has some of the highest rates of maternity deaths in western Europe, at 13 per 100,000 live births, compared with eight in Germany and two in Sweden.