Obesity is one of the "greatest threats" to women of childbearing age in the UK, experts have warned.
A new report showed that more than half of women who die in pregnancy or shortly after birth are overweight or obese.
These women are putting themselves and their babies at risk of complications that could lead to death, the study warned.
The latest report from the Confidential Enquiry into Maternal and Child Health (CEMACH) also called for better communication between staff to cut down the number of avoidable deaths due to other causes.
CEMACH is planning to carry out a national enquiry into obesity in pregnancy as a result of its concerns about the impact on mothers and babies.
Obese pregnant women are more at risk of dying, suffering heart disease, miscarriage, diabetes, infections and thromboembolism, where clots block a vessel elsewhere in the body.
Babies born to obese mothers are more likely to be stillborn, to suffer abnormalities and to be premature.
The study focused on the number of women dying during pregnancy, after miscarriage, birth and after an abortion or ectopic pregnancy, for the three year period 2003/05.
Although the death rate has not changed significantly since 2000, it has risen by around 40% since 1985/87, the study showed.
In 1985/87, the death rate was almost 10 per 100,000 women, rising to almost 14 per 100,000 in 2003/05. The total number of women who died in 1985/87 was 223, rising to 295 in 2003/05.
