According to the U.N. Population Fund, some of the largest gaps between the world's rich and poor are seen in reproductive health, giving poor women and their families fewer opportunities to break out of poverty.
The report cites evidence that shows for the first time that lowering fertility lowers poverty.
"Investing in women is what it comes down to," said the UNFPA's Alexander Marshall, the report's author.
The organization found that people in poor countries do choose to have fewer children if given the chance and that since 1970, developing countries that have lowered their fertility rates and slowed population growth have registered faster economic growth.
Devoting money to health, education and the advancement of women and girls were vital to such achievements, it added.
"There is a vicious circle that links fertility with poverty, " UNFPA Executive Director Thoraya Obaid told the Associated Press.
"To fight poverty, you can't just talk about economic growth by itself. You need to have investment in the social sector in the area of health and education so that it can contribute to economic growth."
With improved general health care and education, children are more likely to survive infancy, which makes women more comfortable with having fewer children, she added.
About one-fifth of the surging economic growth seen in the so-called Asian Tiger countries during the 1980s and early 1990s was attributable to their population and reproductive health programs, the report said.
Obaid said that Brazil, where fertility has been declining for the last 50 years, was another success story, with Mexico and other Latin American countries following its example.
Poverty, poor health and fertility remain highest in the least developed countries where the population has tripled since 1955 and is expected to nearly triple again over the next 50 years, said the "State of World Population 2002" report.
According to the report, around 18.9 percent of the world's population in 1980 lived in absolute poverty.
Half of the world's population — 3 billion people — live on less than $2 (U.S.) a day, Obaid added.
At a news conference to launch the report in London, Obaid said 8 billion condoms are needed every year, not only to help avoid unwanted pregnancies, but also to prevent HIV infection, which disproportionately affects poor women.
"We can only supply 1 billion condoms at the moment," Obaid said. She said money is the main reason more condoms aren't available.
The report said rich countries contributed less than a quarter of the money spent on basic reproductive health programs in the developing world and only paid half the sums of money they had pledged.
By contrast, developing countries contributed 76 percent of the total and about 73 percent of what they had pledged to spend.
Total spending on such programs in 2000 was $10.9 billion, some $6.1 billion less than the total promised.
Obaid said rich countries tended to favor "political and economic issues such as trade" over "issues such as reproductive health and rights of women" when making funding decisions.
"Due attention has to be given to health and education as real engines that can change the situation," she added.
The U.N. Population Fund, launched in 1969, aims to help developing countries find solutions to their population problems. It has three main program areas: reproductive health, including family planning and sexual health; population and development strategies and advocacy.