A saliva test that detects estriol, a type of estrogen, may help determine if a pregnant woman is at risk of premature delivery, researchers report.

Estriol, in addition to being produced by the mother is also produced by the fetus and placenta. Levels increase gradually in pregnancy and then surges in the weeks before labor.

• Investigators measured estriol levels in the saliva of nearly 1,000 pregnant women at 8 US medical centers on a weekly basis starting from the 22nd week of pregnancy.

• Approximately 32% of the women were considered to be at high risk of having a premature baby.

• Women who had two tests in a row that showed elevated estriol were three to four times more likely to experience preterm labor than those with lower levels.

"Regardless of a woman's risk classification, the risk of preterm birth was substantially higher in women with at least one elevated salivary estriol test," according to Dr. R. Phillip Heine of the University of Pittsburgh in Pennsylvania, and colleagues.

According to Dr. Heine, salivary testing offers several advantages over blood tests, such as being simple, convenient, and noninvasive.

"Elevated salivary (estriol) is associated with increased risk of preterm birth in asymptomatic women and symptomatic women who present for evaluation of preterm labor," the authors conclude.

Obstetrics and Gynecology October, 2000;96: 490-497.