Contraceptive use saves the lives of more than 250,000 women each year, either from death in childbirth or unsafe abortions, according to estimates published in The Lancet.
In 2008, 355,000 women died while giving birth or from illegal or dangerous abortions, according to a study published by the medical journal.
It reported that more than 250,000 deaths were averted that year because contraception reduced unwanted pregnancies.
"If all women in developing countries who want to avoid pregnancy use an effective contraceptive method, the number of maternal deaths would fall by a further 30%," the report stated.
The paper, led by Prof John Cleland from the London School of Hygiene and Tropical Medicine, appears in The Lancet on the eve of a "London Summit on Family Planning", promoted by the Bill and Melinda Gates Foundation.
It is campaigning for the rights of 120m women and girls to have access to family planning.
"Increasing contraceptive use in developing countries has cut the number of maternal deaths by 40% over the past 20 years," the paper stated.
It also pointed to the benefits for child health and pregnancies that are planned and spaced out.
The report added: "In developing countries, the risk of prematurity and low birthweight doubles when conception occurs within six months of a previous birth.
“Children born within two years of an elder sibling are 60% more likely to die in infancy than are those born more than two years after their sibling."
The world's population reached 7bn last year and is likely to climb to around 9.3bn by 2050, and more than 10bn by 2100, according to UN estimates.
Demographic growth will be overwhelmingly concentrated in the poorest countries, especially Africa.
