The proportion of women who die during and soon after pregnancy has fallen in the UK, figures show.
However, the assessment by Oxford University suggests up to half of deaths may be avoided by better care and women having the flu jab.
The researchers say doctors need to be more aware of women's wider health during pregnancy and pay attention to the risk of severe infection in labour.
Experts said the situation was improving, but more needed to be done.
The analysis showed 357 women died during pregnancy, or in the six weeks after it ended, between 2010 and 2012.
Around a quarter of the deaths were down to sepsis - a severe infection causing widespread inflammation throughout the body.
The immune system is weaker during pregnancy and the wound caused by the separation of placenta and uterus can be a source of infection.
The report says doctors need to be more aware of the risks.
Meanwhile, one in 11 deaths was down to flu, and the researchers estimate that more than half of them could have been prevented by the flu jab.
Comparison of the data from 2006-08 with 2009-12 shows a fall in the maternal death rate from 11 out of every 100,000 women to 10 out of every 100,000 women.
"It is important to remember that deaths are very rare," said Prof Marian Knight from Oxford University.
She said most progress had been made with deaths resulting directly from the pregnancy with reduced rates of thrombosis, haemorrhage and pre-eclampsia.
However, the indirect deaths - such as suicides, flu and heart disease - have not shifted for the past decade.
Prof Knight said half of deaths were in cases where improvements in care "may" have saved the mother's life.
Three-quarters of deaths were in women who had medical or mental health problems and the research team called for "joint specialist and maternity care" which would see experts in a patient's illness working alongside midwives.
Louise Silverton, from the Royal College of Midwives, commented: "We remain concerned about the high level of deaths amongst women with pre-existing medical conditions, such as a cardiac or neurological conditions.
"We also need more midwives and maternity support workers to deal with the increasing complexity of pregnancy and better teamwork with doctors to provide seamless maternity care."
Prof Alan Cameron, from the Royal College of Obstetricians and Gynaecologists (RCOG), insisted "maternal deaths in the UK are rare".
He said: "Much has been achieved, but more can be done to improve the care of future mothers.
"Sepsis can develop very quickly and it is essential that the symptoms are recognised as early as possible, healthcare professionals need to act quickly and remain vigilant to keep sepsis rates down."
He also encouraged more pregnant women to have the flu jab.
The president of the British Maternal and Fetal Medicine Society, Tim Overton, said: "It is gratifying to see that there has been, yet again, a drop in the overall maternal mortality rate.
"It is clear, however, that the challenge is now to reduce deaths from indirect causes which have remained static for the last 10 years.
"Women with significant medical and psychiatric conditions need to be assessed by multidisciplinary teams enabling risk-stratification before becoming pregnant, and then referred early in pregnancy to the same team allowing timely and appropriate delivery of antenatal care."
The report was part of the Mbrrace project - Mothers and Babies: Reducing Risk through Audit and Confidential Enquiries across the UK.