From ages 21 to 65 — a 44-year stretch — women are supposed to be checked for cervical cancer.

That used to be a simple matter of a getting an annual Pap smear.

No more.

The latest guidelines from an influential government advisory panel, published Tuesday in the Journal of the American Medical Association, recommend screening every three or five years, depending on the woman's age and choice of tests.

While the U.S. Preventive Services Task Force provides a detailed scientific rationale for the updated advice, the panel doesn't address a basic issue: How is a woman supposed to remember that three or five years have passed?

"I've kind of lost track of when I'm supposed to do it," acknowledged Courtney Bean Michaud, 38, of Fort Collins, Colo. "We've moved around a lot because my husband is in the military. There was no reminder."

She glanced at a more urgent preventive-care priority — her two sons, a 5-year-old and a toddler, who were frolicking Tuesday on the lawn next to the Independence Park Visitor Center. "I'm trying to keep track of their shots," she said.

Experts acknowledge the problem.  Cervical cancer screening guidelines have become increasingly complex over the last decade to keep pace with the evolving science and technology. Detection has improved even as screening has become less frequent. But that won't be progress if the unintended consequence is that women lose the habit of getting screened.

"That's a gap, and an important area for research," said Douglas K. Owens, a Stanford University primary care physician and vice chair of the task force. "How do we reach women who haven't been screened regularly, and how can we do better" at helping them keep track?

Cervical cancer, once the leading cancer killer of U.S. women, has become relatively uncommon. About 13,000 women will be diagnosed this year, and about 4,000 women will die, mostly because they didn't get screened or didn't follow up with treatment.

This public health victory is thanks to the low-tech Pap smear, introduced in the 1950s. A scraping of cervical cells is examined under a microscope to spot abnormal ones that can be treated before they turn malignant. Because the test often misses warning signs, women used to be advised to have it every year.

The Pap test remains important, and some doctors still default to  annual screening with it. But the discovery in the 1980s that cervical cancer is caused by certain strains of human papillomavirus (HPV) was transformative.

The discovery led to the development of the HPV vaccine, introduced in 2006.  And it led to a DNA test that detects infection with high-risk HPV strains.

Four years ago, federal regulators approved the HPV test as an alternative — not just an add-on — to screening with the Pap smear.

In draft guidelines issued in 2012, the task force endorsed HPV testing alone, but faced resistance from gynecology groups. Tuesday's final guidance says HPV testing is an option, but so is "co-testing" with the HPV and Pap tests.

Here's the overview:

  • Before age 21, screening should not be done, regardless of sexual history, because studies suggest it would lead to unnecessary treatment of precancerous changes that the immune system would clear naturally.

  • From ages 21 to 29,  Pap smears should be done every three years for women with normal results. HPV tests should not be done because infection is common, but usually cleared. Also, cancer is rare in this age group.

  • From ages 30 to 65, screening should be done every three years with the Pap alone, or every five years with the HPV test alone, or every five years with co-testing.

  • After 65, screening is unnecessary unless the woman has a history of precancerous lesions, or has an inadequate or unknown screening history. Women who have had the cervix removed during hysterectomies also do not need screening.

The recommendations closely align with guidance from expert groups including the American College of Obstetricians and Gynecologists.

"We hope the recommendations foster more discussions between patients and providers about cervical cancer screening … and encourage providers to offer HPV vaccines in their offices," the ob-gyns' group said in a statement.

Even though studies show HPV vaccination of preteens is gradually reducing cervical precancers and infection rates, experts agree vaccinated women should not skip screening.

Fortunately, said Giang T. Nguyen,  executive director of  the University of Pennsylvania's student health service, the value of screening seems to be ingrained even in such women.

"In my experience, they're still thinking that Pap testing is something to do to detect disease, regardless of vaccination status," he said. "I don't think they necessarily understand or think in depth about it."

Or keep careful track.

"In the past, we'd say, 'Come in for a Pap every year.' It was one of the things that made it very easy," Nguyen said. "We do not have a routine for reminding them."