How Accurate Are fFN Tests?

Preterm labor symptoms are alarming to pregnant women and can be a sign that a premature birth is coming. Prematurity, or birth before 37 weeks gestation, is a serious problem that can result in both short-term and long-term disability in the newborn, and it can sometimes lead to the baby's death. The symptoms of preterm labor do not always mean that a woman's body is preparing to deliver early. Interventions to stop preterm labor have their own side effects, so being able to tell the difference between true and false labor in a woman who has not reached term is useful to determine whether she needs interventions.

Enter the fFN test, or fetal fibronectin test. Doctors use fFN tests to determine the likelihood that a woman experiencing preterm labor symptoms will deliver within the next 14 days. But how accurate are fFN tests?

The fFN test is appropriate for women between 22 and 34 weeks gestation who are experiencing symptoms of preterm labor, such as regular contractions, cervical dilation, or pelvic pressure. It is contraindicated for women with multiple fetuses (twins, triplets, or more), a broken amniotic sac, a cervical cerclage (a stitch to keep the cervix closed), a cervix dilated beyond 3 cm, or heavy bleeding. It is not recommended for women without preterm labor symptoms, even if they are considered to be at high risk of premature delivery.

Fetal fibronectin is a protein produced at the junction between the amniotic sac and the uterus. After 24 weeks gestation, it is normally undetectable in samples until about 36 weeks, when it reappears as the body prepares for delivery. The presence of fFN protein means the junction between the amniotic sac and the uterus has been disturbed, possibly as a result of preterm labor.

The fFN test consists of a swab taken from either the posterior portion of the vagina or the area just outside the cervix. It can be repeated if labor symptoms continue every 7-14 days until 34 weeks gestation.

A negative fetal fibronectin test result means that delivery is not imminent. In fact, a woman with a negative test will deliver in the next 14 days less than 1% of the time. If a woman tests negative for the presence of fFN protein, she can be assured that she will almost certainly not deliver within the next 7 to 14 days.

A positive fFN test result, however, does not necessarily mean that a woman will delivery early. Fetal fibronectin protein is always present before preterm delivery, but imminent preterm delivery is not the only cause of detectable levels of fFN protein. A positive test means the woman should be monitored more closely, and her health care provider will use it as only one factor in making treatment decisions.

False positive tests can be caused by anything that disturbs the cervix or uterus. These can include a pelvic exam or sexual intercourse within the previous 24 hours. Lotions, soaps, and douches can interfere with fFN levels, and semen can contain fFN protein. Women scheduled for an fFN test should not have sex nor a pelvic exam for a day or two before the test.

If these guidelines are followed, an inaccurate result can still occur due to human error. Cotton swabs and glass containers can cause false negative results.

Fetal Fibronectin. Lab Tests Online.