Fetal fibronectin (fFN) is a protein that is produced during pregnancy. It is a biological "glue" that attaches the fetal sac to a woman's uterus. It can be detected in a pregnant woman's normal fluids during the first trimester, then it disappears after 22 weeks. The body begins secreting fFN again one to three weeks before labor, as the glue disintegrates in preparation for delivery.
If fFN is present during the critical 22nd through 34th weeks, and there are also signs of labor (contractions, bleeding, or dilation of the cervix), this means that the "glue" is disintegrating ahead of schedule. The mother is then at risk for a pre-term delivery -- labor that occurs before the 37th week of pregnancy.
Why are pre-term deliveries dangerous? A baby's lungs and other major organs finish developing toward the end of pregnancy. A pre-term birth means these organs may not have developed fully, and the baby may not be able to survive on its own. But it is very difficult for doctors to predict which women are at risk of pre-term delivery. The fFN test can give doctors more time to take preventive measures to delay labor as long as possible.