Following a trend among rich nations, the fertility rate in developing countries (search) has dropped below three children per women for the first time, a United Nations report says.

The findings reflect trends, common among many researchers including the U.S. Census Bureau, that suggest the world population boom that had been feared in recent decades would not come to pass. A key factor has been the unexpected drop in the fertility rate.

The U.N. report, released Tuesday, said the fertility rate of 2.9 came as people across developing nations are waiting longer to marry and have children, and are using family planning including contraception (search) more often.

"Women and men in developing countries are marrying later, having fewer children and having them later," a summary of the report said.

The report said that with the fertility rate in 20 developed countries now below the replacement rate, the world was seeing "a major and unprecedented reduction in fertility levels."

Among key findings of the report: In the world's 192 countries, the number of women between the ages of 25 and 29 who are single rose from 15 percent in the 1970s to 24 percent in the 1990s. For men, the increase was from 32 percent to 44 percent.

The report, "World Fertility 2003," said government policies had played a central role in changing reproductive behavior. It cited support by 92 percent of all governments for family planning, and widespread backing for the distribution of contraceptives.

According to the report, the use of contraceptives rose from 38 percent to 52 percent of women. In the developing world, the numbers also rose, from 27 percent to 40 percent.

The report was issued by the U.N. Department of Economic and Social Affairs' Population Division.