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Fetal Fibronectin Test

According to the March of Dimes, half a million babies are born prematurely each year (approximately 10 percent of all pregnancies), making premature birth the second most common cause of infant death in the United States. To help predict preterm delivery, some doctors now suggest that women with symptoms be given the fetal fibronectin (fFN) test.


The fFN test is similar to a Pap smear: your doctor will place a speculum in your vagina and take a swab sample of your cervical secretions. The lab technicians look for a protein called fetal fibronectin, which is produced by the fetal membranes and serves as a sort of glue to attach the fetal sac to the uterine lining. The protein is normally found in your vagina during the first half of your pregnancy, but is absent after the 22nd week until it reappears at the end of the last trimester (one to three weeks before term labor). If it is present between your 22nd and 37th week, it means the glue is disintegrating ahead of schedule and that you may go into preterm labor soon.

The fFN test is not routinely given to women experiencing a normal pregnancy since it has not been shown to accurately predict preterm labor in women who are not at high risk and have no symptoms. However, if you are considered high risk or have symptoms of preterm labor, your doctor will probably order the test. A negative fFN result can put you more at ease and avoid unnecessary interventions such as bedrest or hospitalization. A negative fFN test result is a highly reliable predictor that labor will not occur in the next two weeks; however, a positive result is a less reliable predictor of preterm labor.

A positive fFN test result may prompt your doctor to give you labor-suppressing drugs to hold off delivery for about 48-hours, long enough to administer corticosteroids to speed up the development of your baby's lungs and improve his or her chances of survival.

If you are having symptoms of preterm labor between your 24th and 34th weeks, you have a one in 25 chance of delivering in the next two weeks. If you take the fFN test and receive a negative result, your chances of delivering within the next two weeks go down to one in 125. However, a positive result means your risk of delivering in the next two weeks increases to one in six. If you are considered high risk, you may be asked to take the test every two weeks until you reach 34 weeks or deliver your baby. Women who are already showing symptoms of preterm labor should be tested at 24 to 25 weeks, while women who are high risk without symptoms should be tested as early as 22 weeks and then repeatedly tested as appropriate.

Symptoms of preterm labor include regular uterine contractions that last more than one hour; backache, pain, or pressure; stomach cramping and/or diarrhea; spotting or bloody discharge; and thinning or dilation of the cervix. Early dilation, although something to monitor, is not always an indication of preterm labor. The external opening to the cervix may open slightly, especially in women who have had previous births. However, it is important to look for other changes as well, such as thinning of the cervix and whether or not the internal opening is dilating as well.


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