DENVER -- Most women in their 20s can have a Pap smear every two years instead of annually, say new guidelines that conclude that's enough to catch slow-growing cervical cancer.

The change by the American College of Obstetricians and Gynecologists comes amid a completely separate debate over when regular mammograms to detect breast cancer should begin. The timing of the Pap guidelines is coincidence, said ACOG, which began reviewing its recommendations in late 2007 and published the update Friday in the journal Obstetrics & Gynecology.

The guidelines also say:

Routine Paps should start at age 21. Previously, ACOG had urged a first Pap either within three years of first sexual intercourse or at age 21.

Women 30 and older should wait three years between Paps once they've had three consecutive clear tests. Other national guidelines have long recommended the three-year interval; ACOG had previously backed a two- to three-year wait.

Women with HIV, other immune-weakening conditions or previous cervical abnormalities may need more frequent screening.

"We may not need to screen people as early or as frequently now that we have better pap smears and human papillomavirus virus testing," said Dr. Beth Roland, with Parkside Ob/Gyn in Denver.

Paps can spot pre-cancerous changes in the cervix in time to prevent invasive cancer, and widespread use has halved cervical cancer rates in the U.S. in recent decades. About 11,270 new cases will be diagnosed this year, and about 4,070 women will die from it, according to American Cancer Society estimates.

"Most of them are people who rarely get a pap smear or don't get a pap smear at all," Roland said.

Cervical cancer is caused by certain strains of the extremely common sexually transmitted virus called HPV, for human papillomavirus, which is often caught in a Pap test.

The updated guidelines reflect better understanding of HPV. Infection is high among sexually active teens and young adults. Women's bodies very often fight off an HPV infection on their own without lasting harm, although it can take a year or two. The younger the woman, the more likely that HPV is going to be transient.

Moreover, ACOG cited studies showing no increased risk of cancer developing in women in their 20s if they extended Pap screening from every year to every two years.

In fact, Roland said there can be more harm than good in testing younger women and treating abnormalities.

"The possible harms are additional testing, which can be uncomfortable, even painful at times for women needing a colposcopy, a biopsy, or a leap procedure, in which we do remove a small portion of the cervix," Roland said. "There's risk for bleeding, infection, even potentially early pregnancy loss."

The American Cancer Society, which has been outspoken against new recommendations for mammograms, told 7NEWS these new pap tests recommendations make sense.

"Statistics show cervical cancer is extremely rare in people under age 21. Over diagnosis or misdiagnosis is a huge risk right now," said Dianna Hemphill, a spokeswoman for the Great West Division of the American Cancer Society.

Hemphill said the new recommendations are largely in line with those currently in place with the recommendations of the American Cancer Society.