Since premature birth is the leading cause of death and disability in newborns, researchers have long sought a way to identify preterm labor and stall delivery for as long as possible. Nonetheless, nearly one in ten babies arrives before 37 weeks.

Until recently, experts were hopeful about a method called home uterine activity monitoring (HUAM). For about two hours a day, a woman at risk for preterm labor (one who's carrying two or more babies or who's had a prior preterm delivery, for example) uses an electronic device to detect uterine contractions that she may not even be able to feel. The idea is that if doctors can identify labor early enough, they can take measures to stop it. Over the past few years, however, HUAM has gradually fallen out of favor because there's little evidence that it predicts delivery early enough to prevent it.

Now a recent study of 2,400 pregnant women conducted by Kaiser Permanente, the nation's largest not-for-profit HMO, has added another nail to HUAM's coffin. Researchers found that high-risk women who were tracked with HUAM delivered prematurely just as often  -- 13 to 14 percent of the time  -- as women who were monitored weekly by a nurse. As a result of these findings, doctors may be even less inclined to use HUAM and insurers less likely to cover it.

While the search for a way to prevent preterm birth continues, there's a glimmer of hope: A Food and Drug Administration (FDA) advisory panel recently recommended approval for SalEst, a test that measures the amount of a substance called estriol in saliva. This hormone is secreted by the placenta, and levels rise significantly two or three weeks before delivery.

To use the test, a mother-to-be sends a sample of her saliva to a lab as often as every few weeks starting as early as the fifth month of pregnancy. If high levels of estriol are detected, she's eight times more prone than normal to have preterm labor. Regular levels mean she has only a 2 percent chance of delivering early.

Doctors are likely to prescribe SalEst primarily to women at high risk for preterm delivery, but some may use it for all of their patients, since a quarter of premature births occur among women at low risk. Although final FDA approval was pending at press time, SalEst is expected to be on the market as early as this month.