(Agencies)
Updated: 2008-01-17 08:14

Demographers say there has been at least one boomlet before, around 1990, when annual US births broke 4.1 million for two straight years before dropping to about 3.9 million in the mid-1990s. Adolescent childbearing was up at the time, but so were births among other groups, and experts aren't sure what explained that bump.

The 2006 fertility rate of 2.1 children is the highest level since 1971. To be sure, the fertility rate among Hispanics — 3 children per woman — has been a major contributor. That's the highest rate for any group. In 2006, for the first time, Hispanics accounted for more than 1 million births.

The high rate probably reflects cultural attitudes toward childbirth developed in other countries, experts said. Fertility rates average 2.7 in Central America and 2.4 in South America.

Fertility rates often rise among immigrants who leave their homelands for a better life. For example, the rate among Mexican-born women in the US is 3.2, but the overall rate for Mexico is just 2.4, according to the Pew Hispanic Center, a Washington-based research organization.

"They're more optimistic about their future here," said Jeff Passel, a Pew Center demographer.

Some complain that many illegal immigrants come here purposely to have children.

"The child is an automatic American citizen, thus entitled to all benefits of American citizens. This gives a certain financial incentive for people coming from other countries illegally to have children here," said John Vinson, president of the Virginia-based American Immigration Control Foundation.

Fertility rates were also relatively high for other racial and ethnic groups. The rate rose to 2.1 for blacks and nearly 1.9 for non-Hispanic whites in 2006, according to the CDC.

Fertility levels tend to decline as women become better educated and gain career opportunities, and as they postpone childbirth until they are older. Experts say those factors, along with the legalization of abortion and the expansion of contraception options, explain why the US fertility rate dropped to its lowest point — about 1.7 — in 1976.

But while fertility declines persisted in many other developed nations, the United States saw the reverse: The fertility rate climbed to 2 in 1989 and has hovered around that mark since then, according to federal birth data.

Hans-Peter Kohler, a University of Pennsylvania sociology professor, and others say the difference has more to do with culture than race. For example, white American women have more children than white European — even though many nations in Europe have more family-friendly government policies on parental leave and child care.

But such policies are just one factor in creating a society that produces lots of babies, said Duke University's S. Philip Morgan, a leading fertility researcher.

Other factors include recent declines in contraceptive use here; limited access to abortion in some states; and a 24/7 economy that provides opportunities for mothers to return to work, he said.

Also, it is more common for American women to have babies out of wedlock and more common for couples here to go forward with unwanted pregnancies. And, compared with nations like Italy and Japan, it's more common for American husbands to help out with chores and child care.

There are regional variations in the United States. New England's fertility rates are more like Northern Europe's. American women in the Midwest, South and certain mountain states tend to have more children.

The influence of certain religions in those latter regions is an important factor, said Ron Lesthaeghe, a Belgian demographer who is a visiting professor at the University of Michigan. "Evangelical Protestantism and Mormons," he said.

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