THURSDAY, March 3 (HealthDay News) -- More young people are waiting to have sex, and more women than men are engaging in same-sex encounters, according to a new report detailing Americans' evolving sexual behaviors and preferences.

In statistics compiled from interviews with 13,500 men and women aged 15 to 44, the 2006-2008 National Survey of Family Growth also indicates that more than half of young people under age 24 who have had oral sex did so before having vaginal intercourse.

Other revelations from the survey, released March 3 by the National Center for Health Statistics of the U.S. Centers for Disease Control and Prevention, include three times as many women over 18 reporting being bisexual as men.

The CDC estimates that 19 million sexually transmitted infections occur each year, along with 50,000 new diagnoses of HIV infection. One function of the report is to provide public health researchers with information to develop prevention strategies targeting high-risk groups, lead author Anjani Chandra said.

"Traditionally, people tend to focus on vaginal intercourse, but they sort of forget about other types of sexual behavior," said Chandra, a health scientist at the National Center for Health Statistics, which last released a similar report using data from 2002.

Some of the findings include:

• More young people reported never having any sexual contact with another person. In 2002, about 22 percent of youths aged 15 to 24 said they fit this description, while 27 percent of males and 29 percent of females did so in 2006-2008.
• White youths aged 15 to 24 were more likely (57 percent) than blacks or Hispanics of the same age (39 percent) to report engaging in oral sex before ever having intercourse.
• Twice as many women (12.5 percent) reported any same-sex contact as men (5.2 percent), a number that held steady since 2002.
• About 3.5 percent of women reported they were bisexual, compared to 1.1 percent of men. About 1.1 percent of women and 1.7 percent of men said they were homosexual.
• About 35 percent of females and 44 percent of males reported ever having anal sex with an opposite-sex partner.

Bill Albert, chief program officer for the National Campaign to Prevent Teen and Unplanned Pregnancy, said he is encouraged by the disclosure that more young people have had no sexual contact.

"The adult view is, when it comes to teens and sex . . . that things are bad and getting worse," Albert said. "I don't want to be Pollyanna-ish and say that there's nothing but good news here, but by and large the news is good."

But Albert said he believes that the statistics indicating most youths are engaging in oral sex before intercourse may be nebulous.

"What is 'before' -- an hour, or two days? My strong suspicion here is that sexual activity tends to co-occur . . . they're probably going to have vaginal sex shortly thereafter," he said. "For some young people, they're running the bases backwards. They used to go from more casual to more intimate, but that's not necessarily the case these days."

Sexuality expert Dr. Jennifer Berman said it's not surprising that young people engage in oral sex first because it's now considered a way to gain status and prestige among their peers.

Also, "It often has to do with sexual education or the lack thereof," said Berman, director of the Berman Women's Wellness Center in Beverly Hills, Calif. "Young people don't perceive oral sex as sex and think they're still virgins if there's no penetration."

Chandra and Berman had very different takes on why twice as many women reported same-sex contact as men.

"Whether [the gender discrepancy] is real or they simply have a higher comfort level reporting that, I can't say," Chandra said. "Their comfort . . . may bolster their honesty and disclosure level."

Berman said she feels the disclosure is genuine, but fueled by societal forces.

"In the [sexuality] field and in L.A., we think that same-sex experiences with women are a lot of times related to drugs and alcohol," she said, "or designed and choreographed for men's pleasure."

Berman was critical of the scope and structure of the national report, saying it "left out very productive, active generations" by excluding participants 45 and older and omitting details about sexual habits such as the use of contraceptives, lubricants or sex toys.

"It's an interesting sample," she said. But, "it certainly doesn't enable people in the field to form valid conclusions . . . or form systems or supports."

More information

For more on sexual attraction and orientation, visit the Nemours Foundation.