WALNUT CREEK, Calif. — Adrienne Jones was just nine weeks into her pregnancy when she experienced some bleeding. Her doctor began to monitor her closely. At 24 weeks, she had a shortened cervix, a sign that she might be about to have a risky preterm delivery.

A decade ago, Jones would have been placed in the hospital for weeks, put on an IV and given medications with unpleasant side effects. Instead, Dr. Andrea Gainey did a simple test that revealed Jones was unlikely to go into labor for the next 14 days.

Jones stayed home, relatively worry-free, as Gainey repeated the test every two weeks. Doctors finally induced labor 38 weeks into her pregnancy. Ruth arrived on Nov. 5 weighing a healthy eight pounds.

Without the tests, "it would have been very nerve-wracking because you don't know what's going on inside," Jones said. "Having that peace of mind definitely helped."

Known as "FullTerm, the Fetal Fibronectin Test," the procedure received approval from the Food and Drug Administration in 1998.

It was developed by Sunnyvale, Calif.-based Adeza Biomedical Corp., which was acquired last year by Cytyc.

Yet although the test is now commonly used by doctors, many pregnant women remain unaware of it.

Jones, who is a psychiatric nurse at John Muir Medical Center in Concord, had never heard of it. Neither had many of her colleagues.

"I would definitely tell all pregnant women to educate themselves as much as possible on what new tests are out there," she said. "We as patients are our best advocates."

Each year in the United States, more than 500,000 babies are born prematurely, which means earlier than 37 weeks. That is a premature baby every minute.

Doctors take it seriously because prematurity is the number one cause of neonatal death.

Babies who survive are often at increased risk for cerebral palsy, mental retardation, chronic lung disease, vision and hearing loss, and other problems.

"So we try to jump on preterm labor," Gainey said.

But that has resulted in many unnecessary hospitalizations because it can be difficult to tell the difference between real and false labor contractions.

"We all want to err on the side of caution," Gainey said.

The FullTerm test, similar to a Pap smear, can be performed in a doctor's office. A cotton swab is placed into the cervical opening or back of the vagina to pull out some mucous.

The mucous is tested for fetal fibronectin, a protein released when the placenta starts to detach from the wall of the uterus.

"If the test is negative, the chances of them delivering in the next two weeks is very, very low — in the range of 1 to 5 percent," said Dr. Stuart Lovett, director of maternal fetal medicine at Alta Bates Summit Medical Center.

"So we don't have to give them all of the unpleasant medicine that we gave them before," he said. "We just send them home."

Alta Bates Summit now advises doctors to give the test before referring preterm women to the hospital. The result has been a big reduction in hospitalizations, Lovett said.

Gainey, whose office is across the street from John Muir Medical Center in Walnut Creek, said she can get results back from the John Muir lab in two to three hours.

The test costs about $120 to $200 and is often covered by insurance. A hospital stay can easily exceed $1,000 a night.

Both Gainey and Lovett say they see no reason to use the test on women who are having a standard pregnancy with no sign of problems.

Gainey administers it on women who are 24 to 34 weeks into their pregnancy, who are at-risk for preterm delivery and who are having contractions or other signs that labor is about to begin.

Risk factors for a premature birth include having had a previous preterm delivery, carrying twins or multiple babies, having diabetes, high blood pressure, clotting disorders, and being underweight, obese or very young.

While the test is very good at predicting that a woman will not deliver in the next two weeks, a positive result does not necessarily mean labor will ensue, Gainey noted. Instead, it just indicates that the doctor should check further, she said.

Some gynecologists and obstetricians eschew the test and still prefer to hospitalize all women with signs of preterm labor.

But given the test's high accuracy rate, Jones said the main advantage for her was peace of mind.

Without the test, "I would have been scared that I could go into premature labor at any time," she said. "Every contraction, I would have been thinking something would happen."