More children are born to women older than 35 than to teenagers, a change born of medical science, later marriages and evolving attitudes about motherhood, according to a new study released Thursday. 
 
 The Pew Research Center, citing census and government health statistics, said the trend toward mothers who are older and better educated cuts across all ethnicities in the United States. 
 
 Between 1990 and 2008, the number of births to mothers older than 35 leapt from 368,000 to 603,000. One in seven babies -- or 14 percent of a total of about 4 million births -- were born to older mothers in 2008. Almost one in four were first-time mothers. The vast majority, 71 percent, had at least some college education before giving birth. 
 
 By contrast, births to women younger than 20 declined from 533,000 in 1990 to 441,000 in 2008, or one in 10 babies. The teenage birthrate has declined steadily since 1990, except for a spike in 2006 and 2007. 
 
 The statistics reflect far-reaching changes for women in society, affecting their decisions on when to marry and start families. The average age for marriage has been rising, as has the share of women who have attended college. Women with more education often delay marriage and childbearing while they complete their schooling and establish careers. 
 
 The average age at which women have their first child is 25, a year older than in 1990. 
 
 "It's clear that young adult transitions are being postponed," said Suzanne Bianchi, a sociologist at UCLA. "Children born to highly educated mothers increasingly are born later in life. The mothers are usually married, and they have a much higher chance of raising children in a stable marriage that lasts through a child's childhood." 
 
 The delay in getting married also helps explain two seemingly contradictory trends. The number of unwed mothers has risen sharply in the United States, so that about four out of every 10 births are to unmarried women, which includes most births to women in their early 20s. At the same time, there has been an increase in the number of women who have never had children. 
 
 Experts say some of that may be by choice, and some of it is timing. 
 
 "We're trained to think science can solve all fertility problems," said Wendy Manning, a sociologist at Bowling Green State University, who teaches a class in fertility and family planning. "In fact, there are quite a few limitations." 
 
 The Pew report included a survey on American attitudes toward parenthood that suggests there is less stigma attached to older mothers than once was common. About one in three disapproved of women having babies after age 40, undergoing fertility treatment or remaining childless; the rest said those were good things or made no difference to society. 
 
 Maria Bachman, 42, who runs the Web site MothersOver35.com from her home outside Tucson, said actresses like Sandra Bullock and Nicole Kidman, who are older mothers, have helped create a positive image of women who have children at the onset of middle age. 
 
 "When they're put on the cover of magazines, they're showing it's not too late to be an older mom," said Bachman, who was 37 when she had her first child and 40 when she had her second. "In fact, older moms are considered sexy." 
 
 When asked why they decided to have their first child, 87 percent of the parents in the Pew survey answered, "The joy of having children." But nearly half said, "There wasn't a reason. It just happened." ||||| New mothers in the U.S. are increasingly older and better educated than they were two decades ago, according to a study on the state of American motherhood released Thursday by the Pew Research Center. 
 
 But that doesn't mean women are waiting for the right moment: The study also found that half of mothers surveyed said parenthood "just happened." 
 
 While most women giving birth are doing it within the context of marriage, researchers said a record 41 percent of births were to unmarried women in 2008. That's up from 28 percent in 1990, according to the study, "The New Demography of American Motherhood." The trend crossed major racial and ethnic groups. 
 
 Nearly 14 percent of mothers of newborns were 35 or older two years ago _ and only about 10 percent were in their teens. The age trend was reversed in 1990, when teens had a 13 percent share of births. 
 
 "I think everyone will welcome a decline in births to teens," said D'Vera Cohn, a senior writer on the study. "It's notable that the population of teens is larger than it used to be, so there were more who could have become teen mothers." 
 
 Today, one in seven babies is born to a mother at least 35 years old. In 1990, one in 11 had a mother in that age group. 
 
 Most mothers of newborns (54 percent) had at least some college education in 2008, an increase from 41 percent in 1990. Among mothers 35 or older, 71 percent had at least some college education. 
 
 Improvements in medical care and fertility treatment, along with marriage and childbearing postponed to seek additional education, all factor into the shifts. 
 
 "The rise in women's education levels has changed the profile of the typical mother of a newborn baby," the report said. Cohn added that a lower share of mothers ended their education after high school, "so some of those mothers who would have been high school graduates in 1990 have some college education today." 
 
 The report is based on data from the National Center for Health Statistics and the U.S. Census Bureau, along with a telephone survey in April 2009 of about 1,000 parents, likely parents and other adults of both genders. 
 
 Overall, there were 4.3 million births in the U.S. in 2008, compared with 4.2 million in 1990. The number had risen each year from 2003 to 2007, then dipped in an apparent link to the economic downturn, the researchers said. 
 
 When American parents are asked why they decided to have a child, most cite "The joy of having children," the study said. For nearly half of parents, though, an important explanation is: "It wasn't a decision; it just happened." 
 
 Women surveyed were more likely than men to cite "it just happened" as somewhat or very important in their decision to give birth the first time. 
 
 Stephanie Coontz, director of research and public education for the nonprofit Council on Contemporary Families and a writer who teaches history and family studies at The Evergreen State College in Olympia, Wash., said the rise of single motherhood is significant. 
 
 "It's yet another nail in the coffin in the hope that we can solve the challenges facing us today by shoehorning everyone back into marriages," she said. "One of the big problems with that at this point is very often kids do worse if their mother rushes into a marriage that may be unstable." 
 
 Multiple births associated with the trend toward older motherhood were up sharply, including a 70 percent increase in the twin birth rate from 1980 to 2004. 
 
 "Not only are women in their 30s more likely than younger women to conceive multiples on their own, they also are more likely to undergo fertility treatments, which are linked to births of multiples," the researchers said.
– For the first time, the number of babies born to women over 35 exceeds the number being born to teens, reports the Pew Research Center. Of 2008's 4 million births, one in seven were to older mothers, while one in 10 were to teens. The new, slightly older face of the American mom reflects changes in fertility science, a move toward later marriage, and changing attitudes about childbearing, the Washington Post notes. And the new mom isn't just older, she's also better educated—54% of all new moms, and 71% of the over-35 crowd, have had some college education—and more likely to be unmarried. Some 41% are unwed, up from 28% in 1990. Interestingly, women don't appear to be timing their pregnancies too carefully: About half of the women surveyed said motherhood "just happened," notes the AP. (Click here for a list of celebs who didn't plan on getting pregnant, either.)