Two tests for biochemical markers of preterm delivery are the fetal fibronectin test and the salivary estriol test. However, the salivary estriol is no longer used clinically.
Fetal Fibronectin
Fetal fibronectin is the ?glue? that helps attach the membranes surrounding the baby (the bag of waters) to the lower part of the uterus. Shortly before labor (or sometimes during labor), this lower part of the uterus begins to change shape, causing the membranes to separate from the uterine wall. When this happens, fibronectin is released and mingles with a woman's cervical and vaginal secretions. The fetal fibronectin test measures the fibronectin levels in these secretions.
How Is the Fetal Fibronectin Test Performed?
To test for fibronectin, your doctor or nurse inserts a speculum into your vagina and uses a cotton swab to collect a sample of your cervical or vaginal secretions. The test is quick and easy to do, and does not usually cause much discomfort. The test can't be done if you've had a vaginal exam, bleeding, or intercourse in the last 24 hours because it won't be accurate.
How Effective Is Fetal Fibronectin in Predicting Preterm Delivery?
If you are experiencing signs of preterm labor, a fetal fibronectin test is extremely helpful if it is negative. In studies, less than 10% of women with a negative result delivered before 35 weeks of pregnancy. If your test result is negative, you can often avoid lengthy stays in the hospital because your risk of early delivery is quite small. By contrast, a positive result is not helpful.. Seven out of 10 women with a positive fetal fibronectin will stay pregnant past 35 weeks.
Salivary Estriol
Estriol is a form of estrogen produced by the placenta. About three to five weeks before labor begins (even when the labor is preterm), the amount of estriol in the placenta increases dramatically. The estriol enters the mother's bloodstream and other body fluids, including saliva. Thus, measuring the amount of estriol in a pregnant woman's body fluids should help predict when labor will begin.
How Is the Salivary Estriol Test Done?
The easiest way to measure a mother's estriol level is to take a sample of her saliva, for testing (Sal-Est test). The Sal-Est test is approved by the FDA. However, the test is less reliable than the fetal fibronectin. In studies, many women who received an abnormal result on the test never developed preterm labor. Because of these problems, the of Obstetrics and Gynecology recommends that it only be used for research purposes.
How Does Salivary Estriol Compare to Fetal Fibronectin for Predicting Preterm Delivery?
No study has directly compared testing for fetal fibronectin and salivary estriol to determine which is more effective in predicting preterm delivery. However, the studies of the individual tests suggest that estriol is less reliable than fetal fibronectin, so it is not widely used, and it is not covered by many insurance companies. The fetal fibronectin test has been used to reduce hospital admissions for false preterm labor.
